T HE
RU P T O N O F V E S U V U S
IN
1 87 2,
B!
LU I G I
P R O F E SSO R
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IN TR O DU CT O R ! 8KE TCH O F T HE P R ES E N T S T AT E O F KNO WLE DGE
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V U L CA N I CI T !
T E R R E S T R I AL
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SKE TCH 495 0
IN TR O DU CTO R !
,
.
HE publishers o f this little vol um e in requesting
me to u ndertake a translation of the Incendio
Vesuv iano o f P rofessor P almieri and to acco m pany it
w ith so m e introductory re m ark s have felt j u s tified by the
facts that S ignor P a lmie ri sposition a s a physicist the
great ad v antages w hich his long residence in N aples as a
P rofessor of th e U niversity and fo r many years past
D irector o f the Meteor o logical O bservatory— established
up o n Vesuvius itself prior to the expulsion o f the late
dynasty — have nat u rally caused much w eight to attach
to anything emanating from his pen in reference to that
v olcano
N early forty me m oir s o n various branches of physics
— c h ie fl
— pro
s
electricity
magneti
m
and
meteoro
ogy
l
y
d u c e d since 1 8 4 2 are to be fo u nd u nder P a lm ieri s
name in the U niversal Catalogu e of S cientific P apers of
the R oyal S ociety and of these nine refer to Vesuvi u s
the earliest being entitled P ri m i S tu dii Meteorologici
fa tti sul R O sservatorio Vesuviano published in 1 8 5 3
H e was al so author in conj unction with P ro fessor A
S cacchi of an ela b orate report u pon the Volcanic Region
of Monte Vult u re and on the E arthqu ake (com m only
called o f Melfi) o f 1 8 5 1 Th ese however by no means
exh aust the stock of P a lmieri slabours
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B
T H E LA T E E RUP TI O N
2
V E SU V I U S
O F
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The fo llowing Memoir o f S ignor P al m ieri o n the
eruption o f Vesu vius in A pril of this year
brief
as it is embrace stw o distinct subj ects viz his narrative
a san eye w itness of the actual events of the eruptio n as
they occ u rred u pon the cone and slopes o f the mountain
and his observations as to p u lses e m anati ng from its
interior as indicated by his S eismograph and as to the
electric conditions of the overhanging cloud o f s moke
(so called ) and ashes as indicated by his b ifilar electro
meter both established at the O bservatory T he two last
have but an indirect bearing upon Vulcanology The
narrative o f the events of the eruption is characterised by
exactness o f observation and a sobriety of la ng u a g e —so
widely di ffere nt from the e x aggerated style of sensational
writing that is found in almost all such accounts — that
I do the author no more than j ustice in thus e xpressing
my v iew o f its merits
N o r should a special narration such as this become
less important o r su ffer even in popular estimation by
the fact that so recently my friend P rofessor J P hillips
has given to the world the best general account of
Vesuvius in its historical and some of its scientific
aspects which has yet appeared That monograph
w ith its sparkling style and scholarly digressions as
w ell a sfo r its more direct merits — w ill no doubt become
the manual for m any a fu ture visitor to the volcanic
r egion of N aples ; b u t it like the fo llowing Memoir of
P a lmieri and in common with almost every work that
has appeared o n the subj ect o f Volcanoes contains a
good deal which however interesting and remotely
related to V u lcanology does not properly belong to
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I N T RO D U C T OR ! S K ET C H
3
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the body o f that branch o f cosmical science as I
understand its nature and limits
It tends but little for exa m ple to clear our vie w s
or enlarge our kno w ledge of the vast mechanism in
w hich the Volcano originates and that by which its
visible mass is formed that w e should ascertain the
electric condition of the atmosphere above its eruptive
cone or into what crystallograph ic classes the m ineral
species found about it may be divided : it wi ll help us
but little to know P liny s notions o f ho w P o m peii was
o v erwhelmed or to re engrave pictures assumed to give
the exact shape of the Vesuvian or other cone at
di fferent periods o r its precise altitude w hich are ever
varyi ng abov e the sea E ven much more time and
labour may be spent upon analysing the vapours and
gases o f fum aro lle sand salfatare s than the results can
n o w j ustify
N othing perhaps tends more to the e ffective progress
o f any branch o f observat ional and inductive science
than that w e should endeavour to discern clearly the
scope and bo u ndary of o u r su bj ect
to accord w ith Bacon s maxi m
o is but
T o do s
”
cientice
That once
d imid ium s
tio
P rud ens q u es
haped the roads o r methods of approach become
s
clearer ; and every foothold attained upon these direct
paths enables us to look back u pon such collateral o r
s u bordinate questions as at first perplexed us and find
them so illum inated that they are already probably
solved and by solution again prove to us that we a re
in the right paths
I believe therefore that I shall not do disservice to
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T HE
:
E RUP TI O N
T AT E
O F
V E SU V I U S
.
the gr a nd p o rti o n of cosmical phy sics to w hich volcanic
pheno m ena belong by devoting the fe w pages accorded
ketching what seems
to m e for thi s Introducti o n to s
to me to be the present position of terrestrial V u lca nicity
traci ng the o u tlines and rel ations of the two
a nd
branche s o f scientific investigation — V u lca no logy and
mo logy——b y w hich its true n a ture and part in the
S e is
C o sm o s are ch ie fly to be ascertained
The general term V ulca nic ity properly comprehends
a ll that we see o r know o f actions taking place upon
and m odifying the surface o f o ur globe which are
referable not to forces of origin above the surface and
acting superficially but to causes that have been or are
in operation beneath it It embraces all that H umboldt
has so m e w hat v a guely called
the reactions of the
”
interior of a planet upon its exterior
These reactions show themselves principally and
m ainly i n the m arking out and configuration of the
great continents and ocean beds in the forcing up of
mountain chain s and in the varied phenomena con
sequent thereon as seen in more or less adj acent
formations
These constitute the mechanism w hich has moulded
and fashioned the s u rface of o ur globe from the period
w hen it first became superficially solid and prepared it
as the theatre fo r the a ction of all those superficial
actions— such as those of tides waves rain rivers solar
he a t frost vitality vegetable and animal (passing by
m any others less obvious ) — which perpetually modify
alter or rene w the surface o f our worl d and maintain
the existing regi m en of the great machine and o f its
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I N T RO D U C T O R! S K ET C H
5
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inhabitants These last are the d o m ain o f G eology
properly so called N o geological system can be well
founded o r can completely explain the working o f the
w orld s system as we no w see it that does not start from
V ulcanicity as thus defined ; and this is e q ually true
whether as do most g e o lo g istsw e include within the term
G e ology everything we can know about o ur world as a
w hole e x clusive of what A stronomy teaches as to it
divi d ing Geology in general into P hysical G eology
the boundaries of which are very indistinct— and S trati
graphical G eology whose limits are equally so
It has been often said that Geology in this widest
sense begins where A stronomy or Cosmogony ends its
information as to o u r globe but this is scarcely true
Vulcanicity— o r Geology if w e choose to make it
compr ehend that— must commence its survey o f o u r
w orld as a nebula upon which for u nknown age s
thermic gravitant and che m ical forces were operative
and to the final play o f which the form density and
volume as well as order o f deposition of the di fferent
elements in the order of their chemical combination and
deposition was due w hen first o u r globe became a
liquid o r partly liquid spheroid and which have equally
d etermined the chemical n atu re o f the materials o f the
o u tward rind of the earth that now is and with
these some of the pri m ary conditions that have fixed
the characters nature a nd interdependence o f the ve g e
tables and animals that inhabi t it P hysical A stronomy
and P hysical G eology thro u gh V ulcanicity thus over
lap each other ; the first does not end where the second
begins ; and in every sure attempt to bring G eology to
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THE
6
LA
TE E RUP TI ON
V E SU V I U S
0F
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that pinnacle w hich is the pr e per ideal o f its completed
design — nam ely the interpretation o f o u r w orld s m a
chine as part o f the universal Cosm os (so fa r as that can
ever beco m e known to o u r limited observation and
intelligence ) —w e must carry with u s astronomic con
s
iderations we must keep in view events anterior to the
”
sta tus c o nsistentio r o f Leibnitz nor lose sight of the
fact that the chain of causation is one endless and
unbroken ; that forces first set moving we know not
when or how the dim remoteness o f which imagination
tries to s
ound in shadowy thought like those of the
grand old E astern poem
When the morning stars
”
first sang together
are however changed in form
operative still The light and fragile butterfly whose
glorious garb irradiates the summer zephyr in w hich it
floats has had its power o f flig ht— which is its power
to live— determined by results o f that same chain of
causes that lifted from the depths the mountain on
whose sunny side he floats that has determined the
seasons and the colour of the flower w hose nectar he
sucks and that discharges o r dissipates the storm above
that m ay crush the insect and the blossom in which it
basked A nd thus as has been said it was not all a
myth that in older days affirmed that in some myste
rio ns way the actions and the lives of men were linked
to the stars in their courses
Whatever may have been the manifestations o f
Vulcanicity at former and far remoter epochs o f our
planet and to which I sh all retu r n in the e x isting
state of regimen of and upon o u r globe it shows itself
chiefly in the phenomena of Vol canoes a nd of E arth
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I N T RO D U C T OR ! S KE T CH
7
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quakes which are the subj ects o f Vulcanology and of
S eismology respectively and in principal part also of
this Introduction
The phenomena o f hot springs geysers etc which
might be included under the title o f T h ermo p aeg o lo g y
have certain relations to both but more immediately to
Vulcanolo g y
Le t us now glance at the history and progress of
knowledge in these tw o chief do mains of Vulcanicity
preparatory to a sketch of its existing stage as to both
and by the way attempt to extract a lesson as to the
methods by which such success as has attended our
labours has been achieved
It will be most convenient to treat o f S eismology first
in order
A ristotle — who devotes a larger space of his Fourth
B o o k l l egi K o a ao v to E arthquakes — S eneca P liny S trabo
in the so called classic days and thence no end o f
w riters do w n to a bo u t the end o f the seventeenth
century— amongst w ho m F rom o nd i (1 5 2 7) and Trava
gini (1 679 ) are perhaps the most important no w— hav e
filled volumes with records of facts or what they took to
be such of E arthquakes as handed do w n to or observed
by themselves and with plenty o f hypotheses as to their
nature and origin but sterile of much real kno wledge
read before
H o o ke s D iscourses o f E arthquakes
the R oyal S ociety a bout 1 69 0 afford a curious example
of ho w abuse o f words once given by authority clings as
a hindrance to progress H e had formed no distinct
idea o f what he meant by an E arthquake and so
confusedly mi x es up all elevations o r depressions of a
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T H E LA T E E RUP TI O N
8
V E SU V I U S
or
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conversions
s
ubversions
permanent ch a racter w ith
and transpositions of parts o f the earth
ho w ever
s u dde n o r transitory under the nam e of E arthquakes
A like confu si o n is far from u nco m mon amongst geo
logical w riter s even a t th e present day and examples
m ight be qu oted from very late w r itings of even some
o f the great leaders o f E nglish Geology
From the seventeenth to the m iddle of the eighteenth
century o ne finds floods of hypotheses from Flamsteed
H o ttinger Am o nto ns S tu keley B ecearia P ercival
P riestly and a crowd of others in w hich electricity
then attracting so much attention is often called upon
to supply causation for a something of which no clear
ide a had been formed Count B yland t ssingular work
published in 1 83 5 though showing a curious p a rtia l
insight in point o f advancement m ig ht be put back
into that preceding period
In 1 7 60 appeared the very remarkable P aper in the
t v olu m e o f the
P hilosoph ica l Transactions
fifty firs
o f the R ev J ohn Mitchell o f Ca m bridge in which he
v iews an E arthquake as a s u dden lifting up by a rapid
evolution of steam o r gas beneath o f a portion of the
earth s crust a nd the lateral transfer of this gaseous
bubble beneath the earth s crust bent to follow its
s
hape and m otion o r that of a wave o f liquid rock
beneath like a carpet shaken o n air Great as are
certain collateral merits of Mitchell s P aper showi ng
obser v a ti o n of v a rious sorts much in a d vance of his time
this n otion o f a n E arthqu ake is such as had h e applied
to it e v en the imperfect knowledge o f m echanics a nd
physics then posses sed in a definite manner he could
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I N T RO D U C T OR ! S KE T CH
9
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scarcely have failed to see itsuntenable nature That
the same notion and in a far more extrav a gant form
should have been reproduced in 1 8 4 3 b y Messrs R ogers
by whom the gigantic parallel anticlinals flanks and
valleys o f the whole A ppalachian chain of mountain s
are taken for nothing more than the indurated foldings
and wrinkles o f Mitchell s carpet is o ne of the most
salient examples o f the abuse o f hypothesis untested by
exact science
N either H umbol d t nor D arwin great as were the
opportunities of observation e nj oyed by both can be
supposed to have formed any definite idea of wha t an
E arthquake is ; and the latter who had observed w ell
the e ffects of great sea wav es roll ing in—shore after the
shock did not establish any Clear relation between the
two *
H itherto no o n e appears to have form e d any clear
notion as to w hat an E arthquake is— that is to say any
clear idea of w h a t is the nature of the movement con
s
titu tin g the shock no m atter w hat m a y be the nature
o r origin o f the movement itself
The first gli m mering
of such an idea so fa r as my readi ng has enabled me
to ascertai n is d u e to the penetrating geni u s of D r
Thomas ! oung w ho in his Lectu res on N atural
P hilosophy published in 1 80 7 casually s uggests the
probability that earthqu ake m otions are vibratory and
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f ll
k l g
t
lt t
thq k
h t y
d
t
h
ly gl
d
I
t
thq k
Rp t
k
y ll
t y
g
tt
F o r a u er a cc o un o f the i e ra ure a nd iso r o f a v a nc e m e n
u a es
of
uma n
no w e d e a s t o E a r
e re m e re
a n ce
a t,
,
m u s r e fe r to my F irs e o r o n the F ac so f E a r
ua e s
e or s
,
,
ri is
a n d to the w o r s o f D a u b en , L a ,
s
s
o c ia io n,
y
P il i sa nd o e rs
itsco mp lete hi so r re ma in in ye t to b e w ri e n
,
h
t
B t h A
h lp
t
th
tR p t
.
10
T H E LA T E E RUP TI O N
V E SU V I U S
OF
.
are analogous to those of
This was rendered
somewhat m ore definite by Gay Lussac w h o in an
able paper O n the Chemical Theories of Volcanoes in
the t w enty second vol u me of the A nnales de Ch emie
in 1 8 2 3 says
E n u n mot les tremble m ents de terre
ne s o nt que la propagation d une commotion a travers
la masse de la terre tellement ind é pendante des cavité s
souterraines qu elle S e nte nd rait d a u tant plus loin que
la terre serait plus homog ene
These suggestions of ! oung and of Gay Lussac as
m ay be seen only refer to the m ovement in the more
o r less solid crust o f the earth
But two if not three
other great movements were long known to fre q u ently
accompany earthquake shocks — the recession o f the
sea from the shore j ust about the moment of shock
the terrible sounds o r subterraneous growlings w hich
someti mes preceded sometimes accompanied and some
times followed the shock— and the great sea w ave
which rolls in shore more o r less long after it remained
still unkno w n as to their nature
They had been
recognised only as concomitant but unconnected phe
n o m e na— the more inexplicable because sometimes p re
sent sometimes absent and wholly without any known
m utual beari ng o r community of cause
O n the 9 th February 1 8 4 6 I communicated to the
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tly f m d w ! u ng s id s nd indisti n t
d t
th s f H m b ldt b m s id nt by
in th
W h n th git t i n p d d by n E thq k
s
in gl snt n
t nd s f th th n th is ny sn t s sp t s bt n us
mm ni ti n it isp b bly p p g t d th
gh th
th n ly in
s n is is nv y d th u gh th
th s m m n n
i — Le tu res
N t I l 5L V l I
e
e
e
et
u
a
’
.
ca
e
a
e
ce :
e
ur
ex e
co
d
ho w in istinc
ir e c io n a s
am e
s
!
l/
o
ere
a
ro
,
er a
o
.
e
.
a
o
e re
e
o e
e
er
a
,
“
or
a
a
a
ro
a
e
u
o
co
o
re a o
a
e
a e
e
’
o
ea
o
,
ro
ec o
uc e
o
u
ro u
ro
,
c
a
e
ev
a
ec
a
ua
ar
u
e ea r
e a r
a
e
”
.
e rr a
e
eo
ea r
c
,
I N T RO D U C T OR ! S KE T CH
11
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R oyal Irish A cademy m y P aper
O n the D ynamics o f
E arthquakes printed in Vol ! ! L P art I of the
Transac tions o f that A cademy and published the same
year in which it was my good fortune to have been able
to colligate the observed facts
and bringing the m
together under the light o f the known laws o f produc
tion and propagation o f vibratory waves in elastic solid
liquid and gaseous bodies and o f the productio n and
propagation o f liquid waves o f translation in water
varying in depth to prove that all the phenomena
of earthquake shocks could be accounted for by a single
impulse given at a single centre The definition given
by me in that P aper is that an earthquake is T he
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tra ns
it
wa v esof e la s
tic
f
d irectio n fro m v ertica lly
a
o
wa v e
or
imu th, thro ug h the
f
a ny ce ntre o
w
a rd s to ho r iz o nta lly, in
p
a ttend ed
may be
u
p
on
sea
e
the imp uls
a nd
la nd
st
c ru
imp u ls
e
or
a nd
fro m
so und
w ith
a nd u
p
s
io n in
mp res
u
,
az
co
surfa ce
o
the
mo re tha n
o ne,
a nd
f
ea r th,
a nd
an
y
a ny
fro m
w hic h
tid a l wa v es d ep end e nt
ta nceso
o n c irc ums
f
po
itio n a sto
s
”
.
Thus for exam ple if the imp u lse (whatever may be
its cause ) be delivered somewhere beneath the bed of
the sea all four classes o f earthquake w aves may reach
an observer on shore in succession The elastic wave
o f shock passing through the earth g ene ra lly reaches
him first : its velocity of p ropagation depending upon
the Specific elasticity and the degree of continuity of the
rocky or the incoherent formations or m aterials through
which it passes
U nder conditions pointed o u t by me this elastic
wave may cause an aqueous w ave producing reces
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T H E LA T E E RUP TI ON
12
0 F
V E SU V I U S
.
sion of the sea j ust as it reache s the margin o f sea and
land
If the imp u lse be attended by fractu res of the
e a rth s cr u st or other sufficient causes fo r the impulse to
be c o m m u n icated to the a ir directly o r through the
inter v ening sea ordinary sound waves will reach the
Observer through the air propagate d at the rate o f
feet per second o r thereabouts ; and may also
reach him before or with or soon after the shock itself
through the solid material of the earth ; and lastly if
the i m pulse be sufficient to disturb the sea bottom
above the centre o f i m pulse or other wise to generate an
aq ueous wave of translation that reaches the observer
last rolling in shore as the terrible great sea w ave
o many of the great earthquakes its
w hich has ended s
dimensions and its rate of propagation depending upo n
the magnitude o f the originating i m pulse and upon the
variable dep th of the water It is not my purpose nor
would it be possible w ithin m y limits here to give any
complete account o f the matter contained in that P aper
which in the words o f the P resident of the A cademy
fixed upon an i mm utable basis
u pon a later occasion
the true theory o f E arthq u a ke sW e I Shoul d state ho w
ever that in it I proved the fallacy o f the notion of
vorticose shocks w hich had b een held from the days o f
A ri stotle a nd sho w e d th at the e ffects (such as the
t wi sting on their bases of the Calabrian O belisks ) w hich
,
.
’
,
-
,
,
,
,
,
-
,
,
”
-
-
,
,
,
,
.
,
,
,
,
,
.
,
,
,
Rg t
ll g
.
h l
R I A d
d y
i h R e v C ar e s Gra v e s
T he
,
ca
a n d no w
T rini
Co e e , P r e s
,
’
re s
e n a io n o f th e A c a e m sCu n nin ha m
p
ty
tt
.
.
.
.
.
g
e tc . ,
B ish p
M ed l
o
a
.
th
l
F el o w
o fL im e r ie k
,
en
of
on
T H E LA T E E RUP TI O N
14
or
VESUVI U S
.
The latter consists mainly of a résumé of the acknow
le d ged laws as delivered principally by P oisson o f
fo rmation and propagation o f elastic waves and o f
liquid w a ves by Webers S R ussel and others — the
original matter in this R eport is small — and as respects
the latter portion consists mainly in some proble m s for
finding analytically the position o r depth o f the centre
of disturbance when certain elements o f the wave of
s
hock are given o r have been supposed registered by
se ismometric instruments suc h as that described by
m yself and above refe rred to *
A t the time my
original P aper O n the D ynamics o f E arth quakes w as
p ublished there was little or no exp erimenta l know
ledge as to the actual velocity of transit o f waves
analogous to those o f sound but o f greater amplitude
,
,
.
,
,
,
,
.
,
”
.
,
,
this R po t tho gh I h e n ve befo e ef d to it and
I h
l wa ysf lt th t th Au th did
d
s n w w ith relu t n
ti
T he nly
f n m ade to my l b s pub
m s m inj u s
nly is in th
fo llo wing w ds M ny
lis
h d t h p c ding y
p s nsh e e ga d d th s phe n m n (i E thqu kes) sd in
nd the s bj
g t m su to ib ti ns
t h s l t ly be n
b ght nd o u no tic in M m o ir by M M llet O n the
m e
thqu ake s in w h i h he h s t ea t e d it in
D y n m ic s f E
d t min t m anne nd in m d t il than ny p ding w it
f
m
i
n h
p
I
f
th
t
ll te d w ith th isR ep t it will
P
ap
(
I b eli e f und th t s sp ts th ea thqu k p t th l tt
b
tint p d s in a m th m ti l d ss sm e p o ti ns f th gen l
th y Of e thq k m m nts p e i u sly p ublish d by m s
b
ttd S
ls in th h pt (p 9 0 ) e f ing t S eis
s
m m t y n d th imp t nt sst Ge l o gy tha t might b e (nd s
ince
h
b n t s me t nt) m d f it n m ntio n ism d f th s
ins
t u m nts p i sly p p sd by m no f my nti ip ti n f
th i im p o t nt uss T his is b ut to m o tifyingly su gg sti o f
In
o
e
r
ea
re a
u
ro u
r
re
a ra
e
a e
o ve
e r
o
ua
av e
,
ee
a
,
o
r a
c
a
o ur
a
a
,
r
a
r
e
ar
o
r
e
err
o
e,
o
.
a
_
o
a
,
o e
era
e
.
er
a
e
o
e o
,
e
,
o
r v o
o
or
”
er
r
re ce
or
er
e
a
a
o
ue
a e
a
a
a
a
a
ec
.
,
:
r
,
,
,
u e
ro
e
e
e
ex e
o
ar
,
a
e
re
ca
a
or a
.
r.
e co
or
e
or
u
ec
o,
a
re v o u
e r
re
ov e
e
e
e
r
o,
.
a
v z
e a
e
e
a
,
,
a
,
a
c
o
er
a
e
o re
a
ar
eo r
a
,
o
,
e
’
a
erre
ce
a
e,
r
e
o
r, a
.
r
e
,
o
ar
a e
ev
ra
v
r
o
e,
o
r
a
re e re
e e
e
e
av e
o
ea r
er
a
e er
'
re e
av
av
ce ,
ce .
er o
a
u
,
c a
e
o
e
a
r
o
o
e
e
e
r
a
o
a
e e
e o
c
r
a
e
o
o
ve
th e
P e reant q ui m e a
H a v ing
th e
t
an e
mih i d ixerunt
"
.
l eft this nn ti ed f s m any y s and du ing w h i h
A th h sp ece d d m t th t b o u ne wh e e o
st
ach
u
or
u
a
r
o
e
c
e
or
o
o
a
e ar
r
,
r
r
u r e rro r
c
o e
'
I N TRO D UCTOR Y S K E T CH
15
.
through elastic solids The velocity as deduced fro m
th eory the solid being assumed quite homog eneo usand
co ntinuo us was very great
and might be taken fo r
some o f the harder and denser rock formations at
or
feet per second That these enor
mous velocit ies o f wave transit would be something
near those o f actual earthquake shock seemed probable
to me and was so accepted by H opkins
Thus he says (R eport p
The velocity o f the
sea wave for any probable depth o f the sea will be so
smal l as compared with that o f the vibratory wave that
we may consider the time o f the arrival of the latter
at the place of Observation as coincident with that o f
the departure o f the sea wave from the centre of
”
divergence
.
,
,
,
.
,
.
,
.
,
-
,
,
,
-
.
c er a in
no t ave no w re s a s
s
m us b e o r o en, I S o u
e
i bonu m, ha d I no t o s
oo
rul e, D e m o r tu isn il nis
er v e
v er
o n the
u s ro a
e r re s
a
ri u a
e t o it
In
o ne a m o n s o
re c e n
”
uv ius
if any o ne w i re er to th e a s
a e
P ro es
o r P hillip s
s V es
s
s
,
m o f ear
h as e e n in
T h e m e c a nis
u a e mo v e me n
e innin
an s
T he a e e mine n m a e m a ic ian ,
v es
c o m e en
tig ate d
e
r e m o rs in the s
es
o i
ear h
the
Mr Ho ins, e x a ine
”
in h e
eo r o f v i ra o r m o io n, e t c ( a es2 5 7— 2 5 9 ) — I
e n era
info rma t io n, c o nc u e
a , no t I ,
e nc e o f c o a e ra
m u s, in th e a s
w a s th e di s
c o v e re r o f the T
o f E ar
ua es
ins
eo r
b u t Mr H o
,
o f v i ra o r
eo r
m o io n
th e e ne ra
a ine
a se x
s
or P i i s
ha d no t re ce n
r e err e
my rie n , P ro e s
P ro a
,
o ur
ears ac , a n d I a m
os
e M e mo irs a n d R e o r s o f w e n
to
er e ua e
a , if h e ha s e re
a n inj u sice , h e
co nv ince
o ro u
p
a n d u n w i in
o unin e n io na
ha s o ne s
S ill, the a c sS o w h o w ru e it is a
o
th e
r
t
g d
tly
f g tt
h ld
t
ly
h
t p d
b
d y
b t bl
f
p g
t
b
t th t
l d t by
th k
l d th t
y
thq k
t
tly f d
b k
td
t
lt p b bly tt
f
ll
bg
g
h
thq k
by
pt t h d
l t
pk
pl d th
t
g
l th y
b t y t
pg
t
b
ll t l
pk
h
pl d by
g
l th y
b t y
b bly
f d
f
h ll p
th
p t
t ty f y
th ghly
d th t
h p t
d
t t lly
tt gly
t
f t h
t
th t
th m
T he ill m en d li esa ft
d w ith thei bo nes
T he go o d th e y d o iso ft int
k m y f i nd s
ho uld his a dm i bl b k
s
A nd I may v ent e t
n th e
e ditio n to m o dify t h
eac h
as I d o u bt n t it w ill
p s
s
a ge
’
g t th
.
.
.
.
.
.
-
.
er
v
o
e
,
r
e rre
ur
r
,
.
o
o
r e
a
,
a
o
.
ra
,
r
”
,
e
oo
e
a
T H E LA T E E RUP TI O N
16
or
V E SU V I US
.
P aper (D ynamic
I had suggested
as a n i m portant obj ect to ascertain by actual experiment
w hat m ight be the wave s transit rate in various rocky
and incoherent formations and having proposed thisin
my first R eport upo n the Facts of E arthquake to the
Briti sh A ssociation I w a s enabled by its li b erality
to c o m m ence those experiments in which I was a bly
assisted by my eldest son then quite a lad — D r Juo
Willia m Mallet now P rofessor o f Chemistry at the
U niversity o f Virginia U S ; and to give account of
the results in my second R eport
R eport British
A ssociation for
to that body
Those e x perimen t s were made by producing an im
pulse a t o ne end o f an accurately measured base line
by the explosion o f gunpowder in the formation e x pe
rim e n te d upon a nd noting the time the elastic wave
generated re q uired to pass over that distance upon a
S pecial instruments were d evised
n e a rly level surface
and employed by which the powder was fired and the
time registered by touching a lever which completed
certain galvanic contacts The media o r formations in
w hich these experiments were conducted w ere dam p
sand— as likely to give the minimum rate— and crystal
line rock (granite) as likely to give the maxi mum
The results were received not with doubt but with
m u ch surprise for it at once appeared that the actual
velocity of transit was vastly belo w what theory had
indicated as d erivable fr o m the density and modulus
of elasticity of the material taken as homogeneous
etc
The actual velocities in feet per second found
were :
I n m y or iginal
,
,
,
’
'
”
,
,
.
,
.
,
,
,
,
.
,
,
,
.
,
,
.
,
,
.
,
,
,
,
.
,
I N TRO D U C TOR Y S KE T CH
17
.
In sand
feet per second
In discontinuous and
much
shattered
granite
In more solid granite
This I at once attributed and as it has since been proved
correctly to the loss o f v is v iva and consequently o f
Speed by the d isco ntinuity of the ma teria ls
A nd some indication o f the general truth of the fact
w a s derivable from comparing
the rude previous
approxi m ations to the transit rate o f some great E arth
quakes In the case of that of Lisbon es ti m ated by
Mitchell at
feet per second It w a sstill desirable
to extend similar experiments to the harder classes of
stratified and of contorted rocks This I w a senabled to
carry into e ffect at the gre at ! uarries at H olyhead
hence
t
h
e slate and quartz rocks have bee n obtained
w
(
for the construction o f the A sylu m H arbour there )
taking advantage o f the i m pulses generated at that
period by the great m i nes of powder exploded in these
rocks
The res ults have been published in the P hilosophical
Transactions for 1 861 and 1 862 (A ppendix ) T hey Sho w
that the m ean lowest rate o f w ave transit in those rocks
through m easured ranges o f fro m
to
feet
feet per second and the mean highest
w as
feet per second ; and th e general mean
feet per
second
By a separate train o f experiments on the com
solid
cubes
I
Obtained
o f these rocks
f
li
o
ib
i
t
re s
s
y
p
the mean modulus of elasticity of the material when
C
.
,
,
,
,
.
.
,
.
.
,
,
.
,
,
,
.
,
T H E LA T E E RUP TI ON
18
or
V E SU V I U S
.
perfectly continuous and unshattered with this remark
able result— that in these rocks as they e xi st at H olyhead
eig hties q f the fu ll v e lo c ity of wa ve tra ns
nea r ly s
ev en—
,
,
,
io n d ue to the ma teria l
mis
s
,
if so lid
s islost
a nd co ntinuo u
,
f the heterog eneity a nd d isco ntinuity o f the
rocky masses as they are found piled together in
N ature
I also proved that the w ave transit perio d of the
unshattered material o f these rocks was greatest in a
directio n tra nsverse to the bedding and least in line
parallel with that ; but the e ffect of this in the rocky
m ass itself may be mo r e than counterbalance d by the
discontinuity and imper fect contact of the adj acent
beds
These results indicate therefore that the superficial
rate o f translation o f the solitary sea wave o f earth
quakes may when over very deep w ater e qual o r even
exceed the transit rate (in some cases) o f the elastic
w ave o f shock itself
These results have since received general confirmation
by the careful determinations o f the transit rates of
actual earth quake waves in the rocks o f the Rhine
Country and in H ungary by N O gg erath and S chmidt
re spectively and by those made since by myself in those
In an
o f S ou thern Italy to which I shall again refer
elastic wave propagated from a centre o f impulse in an
infinitely extended volume o f a perfect gas normal
v ibrations
are alone propagated— as is the case with
sound in air
In the case o f like m ovements propagated in elastic
and perfectly homogeneous and isotropic solids the
by
r ea
s
on
o
.
-
,
.
,
,
-
,
,
.
,
,
,
,
.
,
.
,
I N TRO D U CTO R Y S KE T CH
19
.
w ave
possesses both normal and transversal vibrations
and is in so far analogous to the case o f light Mr
H opkins in his R eport above referred to has based
certain speculations upo n the assumed necessary c o
existence o f both orders of vibration in actual earth
quake shocks in the materials of which our earthy crust
is actuall y composed
The existence o f transversal vibration in those mate
rials has not been yet proved experimentally though
there is sufficient ground to preclude our denying their
probable existence
That if they d o exist they play but a very sub o rdi
nate part in the observable phenomena of actual
E arthquake is hi ghly probable
This is the vie w
supported not only by observations o f the e ffects o f
such shocks in N ature but by the theoretic consideration
fects o f discontinuity o f formations in planes o r
o f the e f
beds more o r less transverse to the wave path (or line
j oining the centre of impulse with the mean centre o f
If we
w ave disturbance at any point of its transit)
suppose for illustration sake such an elastic wave
transmitted perpendicularly through a mass o f glass
plates each indefinitely thin and all in absolute contact
with each other but without adhesion o r friction more
o r less o f the transversal vibration of the wave would
be cut o ff and lost at each transit from plate to plate
as the elastic compression can by the conditions be
transmitted only normally o r by d irect push p erp e n
This must take place in
d ic ularly fro m plate to plate
N at u re and to a very great extent and the consideration
with others enabled me generall y to appl y the nor mal
C 2
,
,
,
.
,
.
,
.
,
.
.
,
,
.
,
,
,
,
,
,
,
,
,
.
,
,
,
,
T H E LA T E E RUP TI O N
20
w av e mo tio n
or
V E SU V I U S
.
of
shock alone to my investigation as to
the depth of the centre o f impulse o f the great N e ap o
litan E arthquake o f 1 8 5 7 an account of which was
published in 1 8 62 and to be presently further re
ferred to
H itherto the multitudinous facts o r supposed facts
recorded in num berless accounts o f E arthquakes had
remained almost wholly unclassified and s
o far as th ey
had been discussed — in a very partial manner as inci
dental portions o fgeological treatises— with little attempt
to sift the fabulous from the real o r to connect the
phenomena ad mitted by reference to any general me
c hanic al o r physical causes
I n 1 8 5 0 my first R eport
”
upon the Facts of E arthquakes
called for by the
British A ssociation in 1 84 7 was read and published in
the R eports of that body for that year In this for
the first time the many recorded phenomena of E arth
quakes are classified and the i m portant division of the
phenomena into pri m ary and secondary e ffects of the
shock was established S everal facts o r phenomena
previously held as marvellous o r ine x plicable were
either on sufficient grounds rej ected o r were for the
first time shown susceptible o f explanation A mongst
the more noticeable results were the pointing o ut that
fissures and fractures o f rock o r o f incoherent forma
tions were but secondary e ffects a nd in the latter Were
in fa c t generally o f the nature o f inceptive landslips
This last was not accepted I believe by geologists at
the time ; but the correctness o f the vie ws then pro
pounded as to earth fissure s the nature o f the spouting
from the m of water o r mud— the appearance s taken
,
,
.
,
,
,
,
,
“
.
,
,
.
,
,
,
.
,
,
,
,
,
,
.
,
,
,
,
,
,
.
,
,
.
—
T H E LA T E E RUP TI O N
22
or
V E SU V I U S
.
The first the s u pposed snap a nd ja r occasioned by
the sudden and violent rupture of solid rock masses
to which Mr S crope in his very admirable work on
Volcanoes is disposed to refer the impulse of earthquake
shocks (S crope 2 md edit p
I believe may be
proved on acknowledged physical principles— when ap
plied to the known elasticities and extensibilities of
rocks and keeping in view the small thicknesses frac
tu re d a t the s
a me ins
ta nt— to be capable of only the most
insignificant impulsive effects ; and if we also take into
consideration that strata if so fractured are necessarily
no t free but surrounded by others above and below
any such impulsive e ffect emanating fro m fracture may
be held as no n existent or impossible In the statement
of his views which follows and in obj ectin g to my second
and third possible causes (p 2 9 5 — 2 9 6 headed O bje c
tions to Mallet s Theory
Mr S crope appears to me
to have fallen into the error o f assuming that the nature
o f the im u ls
e or the cause producing it forms any part
p
of
my theory o f earthquake movement or in anywise
affects it I carefully guarded against this in the original
”
P aper T ransa c tio nsR o yal Irish Ac a d e my V o l XXL
p 60 and again p
when I stated it is q uite im
m aterial to the truth of my theory of earthquake
motion what vie w be adopted o r what mechanis m be
assigned to account for the original impulse
A s regards the fifth conj ecture suggested by me I
am no w with better knowledge and larger observation
of volcanic phenomena not prepared to admit any single
explosion at volcanic vents of a magnitude su fficient to
produce by its recoil an earthqu ake wave of any im
,
,
”
,
.
,
,
,
.
.
,
,
,
,
,
,
-
.
,
.
,
’
.
,
,
”
,
.
,
,
.
,
“
.
,
,
.
,
”
,
.
,
,
,
I N TRO D U CTOR Y S KE TC H
23
.
’
portance o r extending to any great distance in the
earth s crust The rock of 20 0 tons weight said to
have b een projected nine miles from the crater o f
Cotopax i which I quoted fro m H umboldt as an ex
16
m
a ple I believe to be as purely mythical as the rock
ix th o f that weight w hich
(bloc rejette) o f perhaps one s
previous to the late eruption lay in the middle of the
A tria dell Cavallo and w hich it was roundly affirmed
had b een blo wn o u t o f the crater but w hich in reality
had a t some time rolled down from near the top of the
cone after having been dislodged from some part o f the
upper lip O f the crater w alls where as itswonderful
hardnessand texture and its enamel like s u rface showed
it had b een roasted for years probably
Nor d o I believe in the sud d en blowing away o f one
half the crater and cone of Vesuvi u s or o f any other
volcano at o ne e ffort however affirm ed
N othin g m ore than conj ecture as to the nature o f
the impul s
e producing great o r small E arthquakes can
I believe asyet be produced That there is some one
master m echanis m productive of most of the i m pulses
o f great sho cks is highly prob a ble b u t that more cause s
than one m ay produce these impulses and that the
causes Operative in small and long repeated Shocks
like those o f Visp Comrie and E ast H addam di ffer
,
’
.
,
,
9
,
'
-
,
,
,
,
,
,
,
-
,
.
,
,
,
.
,
,
.
,
,
,
-
,
A ssuming the p o in t o f ej c tio n o f thi sblo c k (the c t r) to b e
f et a bo v e h e it l ande d a nd ll wing it shigh density s
t fo r large ho ri z nt l
ibl e
nd th a ngl e o f p oj e c t io n th e b e s
d mis
s
sto eac h n ine mile sh o izo nta lly
n ge it m a y b e p rov e d th a t th ism a s
to
w o u ld e qu ir an initia l v l o city o f p j e ti n f f o m
f e t per sco nd o ne asgre t sthat o f sm o o th b o canno n—sho t at
v o l c a no
th e m uzzl e a nd p erfec tly inco nc e iv a ble to b e p ro duc e d by
e
v
e
a
ra
,
e
,
ro
e
,
a
a
a
o
,
e
o
r
e
a
a
,
,
r
e
er
ra e
a
a
r
c
a
a
r
o
o
,
r
—
re
a
:
T H E LA T E E RUP TI O N
24
VES UVI U S
0 F
.
much from those producing great E arthqu akes is almost
certain
We shall be better prepared to assig n all of these
w hen w e have ad m itted a true theory of volcanic action
a nd so are better able to see the intimate relations in
m bet w een seism ic and volcanic actions
m echani s
It is not d ifficult meanwhile to assign the very pro
bable mechanis m o f those comparatively petty reper
eussions which are experienced in close proximity to
volcanic vents when in eruption and which though
certainly seismic in their nature and powerful e nough
as upon the flan ks o f E tna to crack and fissu r e well
built church towers can scarcely be termed E arth
quakes
In my First R eport I stated that almost nothing was
known then o f the distribution of recorded E arthquakes
in time o r in space over o u r globe s surface and I pro
posed the formation and discussion o f a complete
catalogue o f all recorded E arth quakes with this in
Vie w
This w a s approved by the Council of the British
A ssociation and at once undertaken by me with the
zealous and efficient c o operation o f my el dest son D r
J W Mallet
N early the whole o f the Second British
A ssociation R eport of 1 8 5 1 is occ u pied wi th the account
o f the experiments as to the transit rate o f artificially
made shocks in sand and granite as alread y referred to
The Third R eport o f 1 85 2 — 1 8 5 4 c o nzainsthe whole
of this
The E arthquake Catalogue of the British
A ssociation (of which through the lib erality of that
body more than o ne hundred copies were distributed
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I N TRO D U CTOR Y S KETC H
25
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freely ) in which are given in columnar form the fol
lowing particulars from the earliest kno wn dates to the
end o f 1 8 4 2 :
1 The date and time of day as nearly a srecorded
2 The locality o r place of occurrence
3 The direction duration and number of shocks so
far recorded
4
P henomena connected with the sea— great sea
waves tides etc
5 P henomena co nnected with the land— m e teo ro lo
g ic al pheno m ena preceding and s u cceeding
S econdary phenomena— all minor or rem ark
able phenomena recorded
6 The authority for the record
Though most materially assisted by the previous
labours and partial cata logues o fV o n H o ff Cotte H o ff
m an Merrian and above all of P errey the prepara
tion of this catalogue— which demanded visits to the
chief libraries of E urope and the collating o f some
thousands o f authors in various languages and o f all
time — was a work o f great and sustained labour which
except for my dear son s hel p I should never have
found time and power to complete P rofessor P errey
formerly o f the Faculté des S ciences of D ij on now en
r etra it w h o has devoted a long and useful life to assi
d u o u slabours in connection with S eismology was our
great ally ; and his catalogues are so large and com
e for most known parts o f the world after 1 8 4 2 that
l
e
t
p
we were able to arrest o u r o w n catalogue at that date
and take M P erre y sas their continuation up to
The whole British A ssociation Catalogue thus e m
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T H E LA T E E RUP TI ON
26
V E SU V I US
OF
.
braces the long historic period o f fro m 1 60 6
of
vulgar chronology when the first known E arthquake
is recorded to A D 1 85 0 ; and the base o f induction
which it presents as to the facts recorded extends to
between
and
separate E arthquakes My
Fourth R eport
R eports British A ssociation
is occupied principally with the discussion o f this great
catalogue and with that o f several special catalogues
produced by other authors with limited areas o r obj ects
The discussion o f M P e rre y s local catalogues with
those o f others in reference to a supposed prevalent
apparent horizontal direction o f shock in certai n regions
— as to distribution as to season months time of day
o r night relation to state o f tide — the bearings of the
views o f Z ante d e schi and others as to the probable
existence of a terrane tide— the supposed relations of
the occurrence of E arth q uakes upon the age of the
m oon ,as deduced by P errey viz : that l s
t E arth q uakes
occur most frequently at the syzygies ; 2nd that their
frequency increases at the perigee and diminishes at
the apogee ; 3 rd that they are more frequent when the
moon is o n the meridian than when she is 9 0 away
from it— and the views of several authorities as to the
distribution o f E arthquakes in time and in space
occupy the first 4 6 pages O f this R epo rt
It then proceeds to discuss the distribution in time
and in Space as deduced from the full base of the great
catalogue
The results as to time are reduced to curves and
those as to space (or distribution over o ur globe s
surface ) to the gre a t seismic m ap (Mercator s pro
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I N T R O D U C T O R ! S K ET C H
27
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je ctio n) upon which and in acco rdance with certain
principl e s and conventional law s which admit o f the
indication o f both intensity and freq uency all r e corded
E arthquakes have bee n so laid do w n as to pr e sent
a real indication of the distribution o f s e ismic energy
for the w hole historic period and all ov e r the w orld
T he original o f this m a p w hich also sho w s the
Volcano (si z e about 7 feet by 5 fe et) remains for refer
enc e in the custody o f the R oyal S ocie ty A r e duc e d
C opy wa spublished w ith the R e port and to a still mor e
reduced scale has be e n reproduced in other places It
is impossibl e here to do m ore than refer to a fe w o f the
m ore salient points
A s regards distribution in tim e durational seismic
en e rgy m ay b e consid e red as probably constant during
historic ti me though it is probably a decaying e nergy
vie w ed in r e fe renc e to much longer p e riods It do e s
not appear of the nature o f a distinctly p e riodic
forc e
1 Whilst th e minimum paroxys mal int e rval may b e
a year o r two the av e rage int e rval is fro m fiv e
to te n years of comparativ e r e pos e
2 The shorte r int e rvals a re in conn e ction w ith p e riods
o f fe wer E arthquakes no t al w ays w ith those of
least intensity but usually so
8 The alternations of paroxys m and of r e pos e appear
to follo w no absolute law deducible fro m th e se
causes
4 T wo m arked periods o f extre me paroxys m a re
observable in each c e ntury (for the last thre e
centuries ) o ne greater than the other— that of
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28
T HE
LA
TE E RUP TI O N O F V E S U V I U S
.
g re ate st numb e r and intensity occurring about the
middle o f each century and the other to w ards
th e e nd o f each
A s respects se ason th e re app e ar distinct indications
o f a m aximum about the w int e r solstice and e qually so
o f a minimum r a th e r befo r e the autumnal e quinox
It
is no t improbable that there is a remote relation betwee n
E arthquakes and the annual march o f barometric
pressure
W e m ay exp e ct at present one great E arthquake
about every e ight months and w e r e w e posse sse d of a
s
u fli c ie nt report from all parts o f our glob e w e should
probably find scarcely a day pass without a very sensible
E arthquak e occurri ng some wh e r e w hilst as r e gards
still smalle r tremors it might almost b e said that our
globe as a w hole is scarcely e v er free fro m the m
A s respects the distribution o f se ismic en e rgy in
space o f o ur e arth s surface it is that o f bands o f vari
abl e and of great breadth w ith sensible seismic influ
e nce extending to fro m 5
to 1 5 transversely which
v e ry generally follo w :
1 The lines o f elevated tracts w hich m ark and
divid e the great oceanic or terra oceanic basins
(or sa ucers as I have calle d them from their
shallo w ness in r e lation to surface in this discus
sion ) o f the earth s surface
2 A nd in s
o far as these are fr e quently the lines of
mountain chains and these latter those o f vol
c a nic v e nts
so the s e ismic bands are found to
fo llo w thes e likewise Isolate d Volcano e s are
found in these bands also
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THE
30
LA
T E E RUP TI ON O F V E SU V I U S
.
s arches and a concluding chapter o n desiderata and
i nqui ries as to ill understood pheno m ena supposed to
b e conn e cted w ith E arthquakes
re e
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1 84 9 5 0 ,
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I
w a s honour e d
by the reques t to draw
”
E arthquake P heno mena w hic h has
u p th e article
in the first a nd subsequent editions of the
a pp e ar e d
”
A dmiralty Manual o f S ci e ntific Inquiry
O riginally
the subj ect w a sintend e d to have for med part o f the
a r ticl e o n G eology entruste d to Mr D ar win w ho con
u lte d m e upon the subj ect ; and upon m
s
y representing
ho w much E arthquakes had w ithin a short ti me
b e come m atter fo r the m athematician and physicist he
w ith a singleness o f eye to science which it is but just
to place o n record took the necessary steps with the
A dmiralty authorities that E arthquakes should for m a
s e parate article and ad vised its being placed as it w as
in m y h ands
T o record this w ill I believ e be s
uf
fi
ci e nt j ustification for my re ference to this articl e in
w hich a good deal of information as to S eis mo me try is
to b e found
In
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By recurring to Mr H opkins s R eport o n E arthquake
Th e o ry before re mark e d upon R eport o f British A sso
c ia tio n 1 84 7
it w ill be s ee n that the solutions o f the
p roble ms w hich h e th e re gives for finding the d e pth o f
fo cus o f shock are founde d upon the velo city of p rop aya
tio n of the w ave in the inte rior of the m ass the a
pp a rent
ho riz o nta l velo city and the ho riz o nta l d irec tio n of ro ra
p g
p
ya tz o n at any propos e d point being kno w n (
By this it appears plainly that at that ti me
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I N T RO D U C T OR! S K ET C H
31
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Mr H o pkins supposed that it w as the v elo city of
tra ns
la tio n o f the w ave o f shock that did the mischi e f
and no t the velo city of the wa ve p a rtic le o r w a ve itself
A nd fu rther that the former might be obtain e d by
r e fe rence
simply to th e modulus o f e lasticity of the
rock O f any given for mation as ind e e d w a smy o wn
e arliest vie w w hen I produc e d my
D ynamics of E ar th
quake in 1 84 6 From the remarks alre ady made as to
th e vast di ffer e nc e b e t w e e n the actual transit v e locity in
m ore o r less discontinuous rocks — such as they occur in
N atur e— it w i ll be e qually obvious that Mr H opkins s
m e thods asabove mention e d are im practicable even w er e
th e r e no confusion betw e e n the v e locity O f translation O f
th e w av e and that of the w av e particl e o r w av e its e lf
This applies also to the de monstration and diagram
(take n fro m H opkins ) giv e n by P rofesso r P hillips
”
Vesuvius pp 2 5 8
In D ecemb e r 1 8 5 7 occurred the gr e at N eapolitan
E arthquake w hich d e solated a large portion of that
kingdom ; and an opportunity the n arose for p ractically
applying to th e problems of finding the di re ction s o f
earthquak e shock at a giv e n point th rough w hich it
has passed a nd ultimate ly the p osition and d e pth o f
focus other methods which I had se e n from soon
aft e r th e date of publication O f my o riginal P ap e r
w e r e easily practicabl e and the details o f w hich I had
gradually matur e d
Bearing in m ind that in th e cas e o f the normal
vibration in any e lastic solid O f i ndefi nit e di mensions
th e dir e ction o f m otion in space of th e wa v e p a r tic le
coincides in the first semiphase o f the w ave a nd at the
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T HE
LA
TE E RUP TI ON
OF
V E SU V I U S
.
instant of its ma mimnln v e lo city w ith the right line
j oining the particl e and the focus o r centr e o f disturb
anc e it follo w s that in the cas e o f e arthquake s the
no rmal vibratio n o f the w ave of shock is al ways in a
v e rtical pl a ne passing through the focus and any
p o int on th e e arth s surfac e through which the
shock passes (a ssuming for th e present no disturbing
caus e s afte r th e impulse has b ee n given ) and that
at such a point th e m ovement of the w av e particle
n th e first semiphas e o f the w ave is in the sam e
i
di rection or s e nse as that o f translation ; and at the
moment of maximu m velocity the direction in space
of the m otion o f the w ave particl e is that of the right
lin e j oining the poi n t through w hich the w ave has
pass e d w ith the focus or c e ntre of impuls e
If therefor e w e can d e termine the direction of
motion of th e w ave p article in the first s e miphas e and
itsm a ximum velocity w e can obtain fro m any s e lected
point a li n e (that o f e mergence O f the shock) so me
w here in w hic h if pr o long e d beneath the e arth the
focus must have been and if w e c a n Obtain like re
o r tw o
o r m or e selected points w e d e cid e the
u lts f
s
position and th e d e pth of the focus w hich must be in
the int e rs e ction of the s e v e ral lines o f direction of the
w a v e particle motion at e ach poi n t w h e n prolong e d
do w n w ards
N o w as I hav e said it is the v ibra tio n of the wa ve
el
its
f i e the motion of the w ave particle that do e s the
mischi e f— no t the t ransit O f the w ave fro m place to
plac e o n the sur fac e j us t as in the analogous (but no t
similar ) case of a tidal w av e O f translation running u p
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I N T RO D U C T OR ! S KE TC H
33
.
an estuary and p assing a ship anchore d there it is not
the transit up the channel but the w ave form its e lf
i e the m otion o f the w av e particles— that lifts th e ship
se nds he r a little w ay higher up channel drops he r to her
form e r level and sends h er do wn channel again to the
spot she lay i n j ust befor e the arrival o f the w ave
E verything therefore that has been perman e ntly
disturb e d by an earthquake shock has been thus moved
in th e directio n and w ith the maxi m um velocity im
pr e ssed u pon it by the w av e particle in the first s e mi
phas e O f the w ave ; and thus al most everything that
has b e en so disturbed m ay by the application of esta
b lis
h e d dynamical principl e s be m ade to giv e us more
o r l e ss infor mation as to
the velocity O f th e w ave
particl e (o r as w e for shortness say the v elocity O f
shock) the direction of its normal vibration a nd the
position and depth ben e ath the earth s surface fro m
w hich ca me the generati n g impulse
We thus arrive
at these as simply and as surely as w e can infer from
th e position taken by a billiard ball o n w hich certain
forc e s a re kno w n to have acted th e forces th e ms e lv e s
and th e ir di rection or from a broken beam th e p re s
sur e O r the blo w w hich fractur e d it
It is obvious th en that n e arly every obj ect disturb e d
dislocated fractured or ove rthro w n by an earthquake
shock is a sort o f natural seis mo m eter and the bes t
and surest o f all seism o me t e rs if w e only m ake a j udi
cions choice o f the obj ects w hich being found afte r such
a shock w e shall e mploy for o u r purpose This w a sthe
principle which I propos e d to the R oyal S ociety at once
to apply to the e ffects of the then quite recent great
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O
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T H E LA T E E RUP TI ON O F V E S U V I U S
4
.
N eapolitan E arthquake O f 1 8 5 7 and which thro ugh
th e lib e rality and aid o f that body I was enabled to
employ w ith the result I had pretty con fid ently anti
c ip a te d n amely the asc e r tainment o f the approxi mate
d e pth o f the focus
E very shock disturbed obj ect in an earthquake shaken
country is capable of giving so me infor mation as to the
shock that acted u pon it b ut it needs a careful choice
and som e mechanical vo vg to select p rop er and the best
Obj e cts so as to avoid the needl e ss perplexity o fdisturb
ing forc e s no t proper to the shock o r other compli
cations
When properly chosen these natural seismometers or
evidences fitted fo r observation after the shock are of two
great C lasses by w hich the conditions O f the earthquake
motion are discoverable
1 Fractures o r dil c a tio ns (
chie fly in the masonry
f
o f buildings
hich
a
ford two principal sources
w
)
a nd sorts O f infor m ation nam ely :
a
Fro m the observed d irectio nsof fra cturesor
a th and frequ ently
s
s
ures by which the wa ve
fi
p
the a ng le of emerg ence may be im m ediately
i nferred
Infor m ation from the prece d ing united with
k no wn conditions as to the strength o f mat e rials
to resist fra cture by w hich the v elo city O f the
fracturing i mpulse may be calculated
2 T he overthro w o r th e proj ection o r both of bodies
large o r s mall simpl e o r co mplex
From these
w e are e nabled to infe r :
c
By d irect Obs e rvatio n the d irec tio n in
a u muth o f th e w av e path
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I N TRO D U C TOR Y S K E T CH
35
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B y m easure ments o f the hori z ontal a nd
vertical distances O f overthro w o r o f proj e ction
to infer eith e r the v elo city of proj ection o r a ng le
d
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f emerg ence
F ractures by shock pres e nt their planes al ways nearly
in dire ctions transvers e to th e w ave path P roj ectio n s
o r overthro w take place
unl
e ss secondarily distu rb e d )
(
in th e line of th e w av e path o r in the vertical plan e
passing thro ug hyt it : but th e direction o f fall or ov e r
th ro w may be e ither in the sam e direction as th e w ave
e
transit
as the motion of th e w ave particle in the
first semiphase ) o r contrary to it
It is thus obvious that the principal pheno mena
p resented by the e ffe cts of e arthquake shock upon th e
o bj e cts
usually occurring u po n the surfac e of th e
i nhabit e d parts of the e arth resolve th e ms e lves i n to
probl e ms of thr e e ord e rs and are all am e nabl e to
m e chanical treatment v iz
1 P robl e m sr e lating to th e direction and amount of
v e locity producing fractu re or fissur e s
2 P roblems r e lating to th e singl e o r multipli e d
oscillatio ns of bodies consider e d as compound
p e ndulums
3 P roblems referable to the theory of proj ectiles
T he se three m a y combin e in s e veral cas e s and on the
part o f the Obser ver must combin e w ith m e asurements
angular and linear and with g e odetic operations to be
cond ucted in th e shak e n country
T h e m e thods of application in d e tail are described
fully as w ell as their actual application and r e sults in
my w ork published in 1 862 (2 vol s) entitl e d T he
o
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T H E LA T E
36
E R U I’ T I O N
V E SU V I U S
0 F
.
i rst P rincipl e s o f O bservational S e ismology as dev e
lop e d in the R e po rt to th e R oyal S oci e ty o f L ondon of
th e E xpediti o n m ad e by Com m an d of the S oci e ty into
th e I n t e ri o r o f th e K ingdom of N aples to inv e stigat e
th e Circumstances of th e G r e at E arthquake o fD e cemb e r
to the many illustrations O f w hich the p ec u
n ia ry grant in aid of £ 3 0 0 w a s most liberally made
to the publishers (Messrs Chapman and H all ) by the
S oci e ty
It is not my in tention here no r w ould space allo w
o f my
g oing into the details of obse rvation nor of the
d e ductions and conclusions I have r ecord e d in those
volum e s I hav e referr e d to their co n t e nts as marking
th e adv e nt of a ne w m e thod
I hav e ventured to call
it a ne w o rg a no n in the in v estigation of E arthquakes
a nd
through them o f the d e ep inte rior o f our earth ;
and will only add that the m e thod on this its very first
trial proved fertile and succ e ssful T h e depth of focus for
this shock o f D e cember 1 8 5 7 w a sabout s e ven to eight
g e ogr aphical m il e s b e lo w se a lev e l roughly stated It
giv e s m e great pl e asur e to add that m y fri e nd Dr
O ldham D irector G eneral O f the G eological S urvey O f
India has since appli e d these sa me methods to the
ph e n om e na o f the gr e at Cachar E arthquake of the
l 0 th J anuary 1 86 9 and w ith success
The pressure
o fof
ficial duti e s has h e informs m e as yet prev e nt ed
his fully w orki ng out his r e sults but they app e ar so far
to indicate as w e sho uld e xp e ct a d e pth o f focus or
o rigi n consi d e rably great e r than in the E uropea n case
o f 1 85 7
S om e account of D r O ldham s r e sults we re
this y e ar communicated to the G eological S ociety of
F
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T H E LA T E E RUP TI ON O F
38
V E
s
uv I U s
.
apply : in fact many g e ologists app e ar never to have
frame d to the m selves any cl e ar idea o f w hat is a wave
o f any sort liquid o r e lastic
T h e general silence as to
seis mic th eory O f French g e ological w riters is re mark
able to whatever cause attributable It has been said
that French philosophers sho w the mselves little d isposed
to ackno wle d ge o r to follo w the lead o f their foreign
co mpeers in any branch O f science If this be true
o r in s
o far as it ma
y be so it is un w orthy of French
science w hich has such boundless clai ms upon o ur
ho mage I a m disposed to attribute the fact in this
case to other circum stances ; and amongst these to the
s m all extent to w hich o ur language is kno w n amongst
French scienti fic me n
G er m any has sho w n more desire to cultivate this
branch O f science
Although as yet the distinct
enunciation O f its fundam e ntal principles has but
sparsely foun d its w a y into her text books several able
such as those o f S ch midt and of
m onographs
o
H ottinger prove ho w completely so m e O f her p hilo s
The
p hershave m astered and h o w w ell applied the m
hom so
me n o f science o f N orth e rn Italy am ongst w
m any glorious names are to be found o n the roll O f
discovery have sho w n themselves quite alive to the
i mportance o f S eism ology ; and I know o f no m ore clear
ex act and popul a r e xposition o f its princi ples and
application and of its cosmical relations than is to be
found in a s m all volum e by P ro fessor Gerolamo
Boccar d o published at G e noa in 1 869 entitled
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S is
mop iro log ia T erremo ti, V ulca ni
suo lo , sagg io d i
a na
teo ria
e
lente
s
o cillaz io ne
d i G eog rap hia F is
ica
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del
I N TR O D U C TOR Y S KE TC H
39
.
My obj ect s
o far
has be e n to m ark the progress o f
ascertaine d theoretic n otions as to S eis mology I have
therefore passed w ithout notice m any speculative
monographs and the treatment up o n E arthqu ak e s
w hether speculative o r historical and how
ever able
th at constitutes a prominent feature o f nearly a ll
systematic w orks on G eology
That w hich m ay be at pre sent vie w ed as achieved
and c e rtainly ascertained in th e oretic S eismology is the
clea r conception o f the natur e o f earthquake motion ;
the r e lations to it o f gr e at sea o r other w ater w av e
commotions ; the relations to it o f sound w aves— as to
w hich how ever m ore r e mains to be kno w n ; a nd th e
r elations o f all these to seco n dar
y e ffects tending in
v arious w ays to modify more o r less the topographic
and other conditions o f the land o r sea bottom
A nd
in descriptive S eis mology the present distribution o f
th e ear thquake bands o r regions o f greatest seism ic
prevalence and activity a re tolerably ascertained and
their connection w ith volcanic lin e s and those o f elevation
r e nd e r e d m ore evident Vi e w e d alone nothing can ye t
b e said to be absolutely asc e rtained as to the imm e
T he
d iate ly antecedent cause o r causes of the impulse
function o f E arthquake as part O f the cosmical m achine
has beco me m ore clear as th e distinctive boundaries
b e t w e en E arthquake and per manent elevation O f the
e arth h ave been m ad e e vid e nt ; and it has been se e n
that E arthquake ho w ever conte mporaneous occasionally
w ith p e r m anent elevation is not the cause tho u gh it
m ay be o ne o f the consequ e nc e s o f the sam e forc e s
that an infi nite
w hich produce elevation ; a nd thus
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T H E LA T E E RUP TI ON
4 0
0 F
V E SU V I U S
.
numb e r of E arthquakes h o we v e r viol e nt and acting
th rough ho w e ver prolong e d a time can never act as an
unless ind e ed on that
a g e nt of p e rman e nt e l e vation
minut e scal e in w hich surface e levation m ay aris e from
secon dary e ffe cts lik e that o f the U llah Bund
Much re mains to b e done and much ma y b e exp e cted
e v e n from th e continuatio n if done in a syste matic and
o rganised m anner of the statistic record o f E arthquakes
in conn e ction w ith thos e other branch e s o f cosmical
statistics Clim atology Meteorology Terrestrial Magne
tis
m e tc the Observation o f w hich is already to a c e rtain
extent organised ov e r a larg e portion o f th e glob e
A nd no w let us look back for a m om e nt to ask Ho w
by wh at mental path of discovery hav e w e arriv e d at
w hat w e hav e passed in revie w T
The facts of E arthquak e s hav e been before m en fo r
op e n s e cre ts as N atur e s facts hav e
u nkno w n ages
”
b e e n w ell called ; but e y e s had they and saw not
F acts vie w e d through th e ha z e of sup e rstition or O f
foregon e notions of w hat N ature o ug ht to do ceas e to b e
facts When after the the great Calabrian E arthquake
the R oyal A cademy o f N aples sent forth its
o f 1 783
commission o f its learned members to examine into the
ef
fects th e y had spread aro und the m in sad p rofusion
all that w a sn e c e ssary to hav e e nabl e d th e m to arrive
at a t rue notion o f the natu re of the shock and thenc e
a sound explanation of th e vari e d and gre at secondary
ef
fe cts th e y w itnessed and of w hich they have l e ft us
th e re cords in th e ir R eport and the eng ravings illus
t ra tiv e of it
But w e look in vai n for any light ; the
th ings se e n often with distortion o r e xagger a tion are
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I
N TRO D U CTOR Y S KE T CH
4 1
.
heaped together as in the phantasmagoria o f a w i ld and
terrible d rea m fro m w hich n e ither order nor conclusion
follo w
Why w a sthis ? Why w e re th e s e e min e nt sa va ntsno
mor e successful in explaining w hat they saw than
th e ignorant peasants they found in the Calabrian
m ountains
B e cause physical sci e nce its e lf w a s not su ffici e ntly
advanc e d no doubt ; but also b e caus e th e y h a d no
notion o f applying such sci e nc e as th e y had to the v e ry
c e n tral point its e lf o f the main probl e m before th e m
free d from all possible adv e ntitious conditions and so as
it w e r e attacking it in the r e ar H o w di ffe r e n t migh t
hav e b e e n th e r e sult of th e i r labours had th e y b e gun by
aski ng th e ms e lv e s What I S an earthquak e ? Can w e not
try to find out w hat it is by obs e rving a nd mea suring
e e th e convers e mode of dealing
w hat it has don e ?W e s
w ith N atur e in Torricelli
N ature abhors a vacuum
P ossibly
w a s told him as the w isdom of his day
but her abhorrenc e is limited for I find it is mea sured by
th e pr e ssur e of a column of w at e r of thirty four fe et in
h e ight \V e n e e d not pursu e th e sto r y with P ascal u p
to th e top of the P uy d e D ome
This lesson is instructiv e g en e rally to all inv e stigators
and particularly here ; for Vulcanology to which w e
are about no w to tu rn has occupi e d u ntil almost to d ay
m uch the sam e position th at S eismology did in those O f
th e N eapolitan Co mmissioners
Whol e librari e s have been w ritt e n w ith respect to it
d e aling w ith q uality but mea su re and q ua ntity r e main
to be applied to it
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T H E LA T E E RUP TI ON O F V E SU V I U S
4 2
.
a v e ry pr e po n d e rant class in the civilised w orld
no kno w l e d g e is of much int e rest or v a lu e that does not
”
ur
point to w hat is call e d a practical r e sult o ne m ea s
ab le i nto utility o r coin I do not stop to remark as to
th e bad or as to c e rtain good results o f this tendency of
mind ; but I may ventur e to point o u t to all that the
e xact kno w l e dg e of the natur e o f e arthquake m otion
e v e n during the short time that it has b e come kno wn
has not been barren in r e sults absolutely practical and
u tilitarian
T he minut e investigation o f the destruction
o f buildings
e tc
and the deductions that have b e en
made as to th e r e lations b e tw een the form h eight ma
te rials m e thods o f building combination of timber and
o f masonry and m any other architectural o r constructive
conditions have made it certain no w that earthquake
proof houses and other edifices can b e constructed with
facility and at no great increase if any at all o f cost I
can affir m that there is no physical necessity why in fre
quently and violently shaken countries such as S o uth e rn
Italy o r th e O riental e nd gen e rally o f the Mediterranean
v icti ms should here after continue by thousands to b e
sacrificed by th e fall of their ill designed and badly
built houses
”
W e r e a Building A ct properly framed put in
forc e by th e Italian G ov e rn m ent in the Basilicatas and
Capitanata e tc so that ne w houses o r existing ones
w hen r e built should be so in accordance w ith certain
simple rul e s a no t very distant ti me can be forese en
w h e n E ar thqu a k e s passi ng through these rich and
fe rtil e but no w frequently sorely afflicted regions should
co m e a nd g o having l e ft but littl e trace o f ruin or
T
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I N TRO D U C TOR Y S K E TC H
4 3
.
d e ath behind S ome d isaste rs ther e m u st al w ays b e
for w e cannot m ake the flanks o f mountains no r the
b e ds of torrents e tc al w ays secur e ; but the main
mortality o f all E arthquak e s is in the hous e s o r oth e r
inhabited buildings Make these proof and the w hol e
sale sl aughter is a t an end
The princi ples w e hav e e stablished have been thus
practicall y applied in another dir e ction T he J apan e s e
G overnment w ith the k e e n and rapid perception O f th e
po wers inherent in European sci e nc e which characte ris e s
no w that w onderful p e opl e has comm e nced to illu m i
nate its coasts by lighthouses constructed a fter the best
E uropean models But J apan is greatly convulsed by
earthquake s a nd lighthouses as bei ng lofty bu ildings
are p e culiarly liabl e to be destroyed by th e m
T he engin e e r o f the J apanese G ov e r nment for thes e
lightsMr Thomas S tevenson C E (one of th e e ngin e e rs
to th e Com missioners of N orth e rn Lights ) w a s in
structe d to have regard in th e design o f those light
houses to their exposure to shock I w a sconsulte d by
Mr S te v e nson as to the gen e ral principl e s to b e observ e d
and those edifices hav e b e e n constructed so th at th e y
a re presumedly proof against th e most viol e nt shocks
likely to visit J apan not perhaps upon the b e st possi
b le plan but upon such as is truly based upon th e p rin
Mr S te venson has published
c ip le sI have develope d
some account O f their construction
T he e arthquak e regions of S outh A merica m ight
w ith incalculabl e benefit apply those ideas ; and in
d e ed they have been to so me extent already ap plied
by my friend Mr Willia m Lloyd Me mber Of the
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T H E LA T E E RUP TI ON O F V E SU V I U S
4 4
.
I nstitution of Civil Engi neers to th e N e w Custo m H ous e s
construct e d fro m his d e signs at Valparaiso
A s o ne o f thes e utilitarian vi e w s and an im
portan t o ne it w ill occur to m any to ask — Can the
mom e nt of th e occur re nc e o r th e d e gr e e of intensity
of e arthquak e shock b e pr e dicted o r is it probabl e
th at at a futur e day w e may b e able to predict
th e m ? A t pr e sent a ny prediction e ith e r of the
o ne or th e oth e r
is impossible ; and those few who
h a v e profe ss e d the m s e lves in possession O f suffi ci ent
grounds fo r such prediction a re dec e iv e rs or d e c e ived
N or is it lik ely that for very many y e ars to com e if ever
science shall hav e advanc e d so as to r e nder any such
p rediction possibl e ; but it is neith e r impossi bl e no r
improbabl e that th e tim e shall arrive w h e n within
certain p e rhaps w ide limits as to space previous time
and i n stan t of occurrenc e such fore w arnings may b e
obtainabl e
E arthquak e s like storms and temp e sts and nearly all
changes of w e ather are not p e riodic ph e nomena nor
a
solutely
unc
e rtain or so to
say
accid
e ntal as to
b
t
e
y
recurrence
Th e y are quasi periodic that is to say som e Of th eir
con d itions as to causation rest upon a r e ally periodic
basi s as for e xampl e the re curr e nc e o fstorms upon the
p e riodic march o f th e e arth and sun and m oon e tc
a nd th e r e curr e nce
o f E arthquak e s
upon the secular
cooling of our e ar th ; but th e conditions in both are so
num e rous and complicat e d w ith particular s that we
can n ot fully analys e th e m — h e nc e can not reduc e the
phenom e na to law and S O cannot predict r e cur renc e
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T H E LA T E E RUP TI ON O F V E SU V I U S
4 6
.
may say N apl e s and the P hle g rman field s g e nerally
hav e never e xperienced a shock as gr e at as the very
mod e rate o ne that w ould overset th e s e columns A
shock w hos e w av e par ticl e had a hori z ontal velocity of
ritish )
f
e et (
B
e r second w ould ov e rturn
o nly about 3
p
%
th e s e columns ; w hich is only abou t o ne fourth the
v elocity (w ithin th e ni e iz o se ismic are a) of the great
shock o f 1 8 5 7 that produced w ide spread destruction
in the Basilicatas and n o t enough to thro w do w n any
reasonably w ell built house of moderate height
N apl e s so far as E arthquake is concerned w heth e r
comi ng fro m the throes of Vesuvius or e lse wh e r e has a
pr e tty good chance of safe ty S he may possibly (though
not probably ) b e some day smoth e r e d in a shes ; but is
in littl e danger of being shaken to th e earth D uri ng
this time th e re hav e be e n taking place larg e r eruptions
o f Vesuvius and e arthquak e shocks fro m oth e r centr e s
togeth e r probably about th e same number of ti me s as
the numb e rs of thos e years w hen thos e columns hav e
be e n more or less shaken
W e may th e refore affir m that the probability (on the
basis of this experience o nly) is say 1 2 0 to 1 that
th e n e xt shock w h e th e r de riv e d from Vesuvius or e ls e
w h e r e that m a y shak e P o z z uoli w ill b e one l e ss in
po we r than w ould be nee d ed to ov e rturn the sh afts of
th e T e mpl e of S erapis there
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L et us no w turn to the second branch of our subj e ct
v iz
Vulcanol o gy upon w hich as ye t w e hav e secured
l e ss firm standing ground than w e hav e seen w e possess
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I N TRO D U C TOR Y S K ET CH
4 7
.
in S eismology for which reason w e took that first into
consideration
It is the part o f Vulcanology to c o o rdinate and e x
plain all the phenomena O f past or pr e sent times visible
o n o u r globe w hich a re e vidences Of th e e xistence and
action wheth e r local or g e neral o f temperatures w ithin
our globe greatly in exc e ss of those of the surfac e
and w hich reach the fusing points o f vario us min e ral
compounds as found arriving h e at e d or fus e d at the
surfac e
The stratigraphic g e ologist se e s that such h e ate d or
fused mass e s hav e com e up from b e neath throughout
e ve ry e poch that h e c an trace ; but he cannot fail to
discern mor e o r less a chang e in th e order or character
o f those o u tc o m in s as h e traces them fro m th e lo w e st
g
He
and Oldest formations to those O f th e pr e sent day
s e es immens e outpouri ngs of g ranitoid o r p o rp h yrytic
rocks th at hav e w e lled up and o v erflo we d the old e st
strata — huge dyke s
filling mil e s of fissures that had b e e n
previously open e d for th e r e ception o f th e molte n matte r
that h as fill e d them and o ften passing thro u gh thos e
mass e s o f previously outpoured rock ; lat e r h e s e e s hug e
tabl e s of basaltic rock poured forth ov e r all O n e grand
charact e ristic com m on to all thes e — commonly call e d plu
tonic products— b e i ng that wheth e r th e y w er e poure d
forth over the surfac e or inj ected into caviti e s in o th e r
rocks the m ovements of the fu s e d material w ere o n
ive
th e whole hydrostatic and no t exp lo s
A t the present day whatever other e vid e nc e s we hav e
of high temperatur e b e lo w o u r globe s surface that
w hich pri m arily fixes th e e ye of the geologist is the
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T H E LA T E E RU P TI ON O F V E SU V I U S
4 8
.
characteristic as w e see it in activity
But though th e r e is this great characte r
isexp lo s
ive
is
tic di ffe r e nc e b e t w e e n the pluton ic and th e volcanic
actio n s a nd th e i r products th e tw o w h e n looked at
larg e ly a re s e e n so to inosculate that it is impossible
not to r e fe r th e m to an agency common to both ho w eve r
c h ang e d the mod e s O f its action have b e en betw een the
e a rli e st e pochs O f w hich traces a re p re sented to us and
the present day
To us littl e m e n w h o as H ersch e ll h asw ell said in
re fe rri n g to th e m e thods of measuri ng the si z e o f o u r
glob e
can never see it all at o nc e but must cre e p
”
like mite s ab o ut its surface the Volcano in th e stu pe n
dous grand e ur of its e ffe cts t ends to fix itse lf in our
minds in e x a gg e rated p roportions to its true plac e in
th e cosmic machine ; and in fact n e arly all w ho hav e
sought to e x pound its nature and mode o f origination
hav e o ccupi e d th e mselves far too exclusively w ith de
scribing a nd th e orising u pon th e strange and varied
ph e nom e na which the volcanic con e itself and its
eruptions pre s e nt and too often in the splendour and
variety of these hav e very much lost sight of w hat
o ught to b e th e c e ntre point o f all such studies nam ely
to arriv e at som e sound kno wledg e O f w hat is the
N or has
p rimma mo bile of all th e se wond e rful e fforts
the distinction b e e n very cl e arly se e n b e t w een the mai n
ph e n om e na p re s e nt e d at a nd about volcanic active
m o n th s w hich can be e mployed to e lucidate the natur e
o f th e causation at w o rk
far b e lo w and those most
varied and curious and in oth e r r e sp e cts most pregnant
and instr uctiv e ph e nom e na mechanical and che mical
V o lcano
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I
N T R O D U C T OR ! S K E T C H
4 9
.
w hich
are called into action in and by the ej e cte d
m atte r O f the volcanic cone after its ej ection
It c a n
help usbut little or very indirectly in getting at a true
conc e ption o f the nature and source o f the h e at itse lf
o f the Volcano to exa min e for exam le all the curious
p
circumstances that are seen in the move ments and
changes in the lava that has alrea d y flo wed from its
m outh ; but it w ould be of great i mportance if w e can
ascertain by any for m o f Observation around the cone
from w hat depth it h as co me o r at what depth the
igneous origin lies
The physician ende avouring to ascertai n the real na
t ur e o f s mall pox o r m easl e s w ill scarcely m ake much
progress who ho wever curiously o r m inutely confin e s
his attention to the pustul e s that he sees u pon the skin
! e t the Volcano o r rath e r all volcanic activity a s
no w operative upon our glob e is as it w ere an e xp e ri
m e nt of N at ure s o w n perp e tually going o n befor e us
the r e sults o f which if w e ll chosen— that is as Bacon
says by keeping to the main and neglecting the acci
dents— c an w hen Colligate d and correctly re a soned u pon
in relatio n to o u r planet as a w hole give u sthe k e y to
the enigma o f terrestrial V ulcanicity in its most g e n e ral
sense and at every epoch o f o ur world s geognostic
history and sho w us its true pl a ce and use in the cos
L et us glanc e at the history of past
mical m achine
speculation o n this subj e ct from w hich so little real
kno w l e dge is to be d e rived and then at the sali e n t
facts of V ulcanology as no w s e en upon o ur earth and
finally s
e e if we can connect these with other great cos
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E
T H E LA T E E RUP TI O N O F V E SU V I U S
50
.
mical co nditions so as to arrive at a co nsist e nt ex plana
tion in h armo ny w i th all
W e gain nothi ng absol u t e ly fro m the kno wl e dge of
a ncients
as to Volcanoes i n E urop e at
th e s
o call e d
l e ast w h e re a lo ne historic r e cords likely to r e fe r to th e m
The Volcanoes of E urope a re fe w and w idely
e xist
scatte red The G reeks sa w but littl e o f th e m and the
R om ans w ere all and at all times most singularly u no b
s e rvant of natural ph e no m ena
C ae sar nev e r me ntions th e e xistence in France of the
Volcano e s of A uvergn e so m uch like thos e h e must ha ve
seen i n Italy and S icily ; and R oman w rit e rs pass in
sil e nc e that great V olcanic r e gion though i nhabite d by
them and their langu ag e impress e d upon the plac e s as
rs
e ;
V o lvic (v o lca no v icus
seems
w
ith
othe
to
indicat
)
and though ther e is so me reason to b e lieve that o ne or
other of the P uys w a sin activity w ithin the firs t five
hund red years of our epoch the notices w hich H umboldt
aniu sP liny
a nd others have coll e cted as from P lato P a u s
O vi d e tc teach nothing
Whatever of mere sp e culation there m ay have been
volcanic theory o r w hat has passed for such th e re
w a snone b e fore 1 7 0 0 w hen L em ery brought for ward a
trivial e xperiment the acceptance o f w hich even for a
and it
moment a s a sufficient caus e for volcanic heat (
retarded other or tru e r vie w s for ye ars ) w e can no w o nly
B re islak s origi n in th e burni ng of sub ter
w on d e r at
r a ne a n petrol e um o r lik e combustibles w a sscarcely l e ss
absurd than Lé mé ry ssulphur and iron filings
D avy in the plenitude of his fame , and full o f the
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I N TR O D U CTORY S KETC H
51
.
intense che mical activities o f the metals o f the alkalies
w hich he had j ust isolate d thre w a ne w but transient
verisimilitude upon the so called che mical theory of V o l
canoes b y as
c rib ing the source o f heat to the oxidation
o f those metals assum e d to e xist in vast unproved and
unindicated m asses in th e i nterior of the earth But
D avy h ad too clear an int e llect not to see th e base
less nature o f his o w n hypothesis which in his last w o rk
the
Consolations in Travel he for mally recant e d ;
and it only survived him in the long continu e d though
unconvincing advocacy of D r D aub eny S o far the
origin o f the heat had b e e n sought al w ays in the crude
notion Of so m e sort o f f ue l co ns
umed w hether that w e re
petroleum o r potassiu m and sodiu m ; but as no fuel w a s
to be fou nd nor any indicated by the products so far as
kno w n of the volcanic heat so w hat has been call e d
the mechanical theory in a variety o f shapes took its
plac e
This in wh atever form takes its lava and other
heated products o f the v o lc an o ready mad e from a
u niv e rsal ocean o f liquid material w hich it suppos e s
constitut e s the interior or nucl e us of o ur glob e and
w hich is only skinned over by a thin solid crust o f
cool e d and consolidated rock which w asvariably e sti
m ated a t fro m fourteen to p erhaps fifty m iles in thick
n ess H ere w a sa boundl e ss supply of m ore than heat
o f hot lav a ready m a d e th e existence o f which at th e se
m od e rate depths the then state o f kno w ledge o f hypogeal
temperature w hich w assuppos e d to g o on incre asing
with depth at the rate of about 1 Fahrenheit for eve r y
thirty or forty feet see me d quite to sustai n
E 2
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T H E LA T E E R U PT I O N
52
0F
V E
s
U V IU S
.
The di fficulty re m ained ho w w a s this fie ry oce an
b ro u ght to th e surface or far abov e it ? To account
for this tw o m ain notions pr e vail e d and indeed have
not c e ased to pr e vail S om e unkno wn e lastic gases or
vapour forced it u p through fissures o r rents pre
e xistent o r produced by th e te nsion of the elastic and
liquid pr e ssur e b elo w
The form in which this vi e w took m ost consistency
and appro a ching m ost n e arly to truth finds the elastic
vapour in st e am g e n e rat e d fro m w ater passed dow n
thro u gh fissures fro m the sea o r from the land surface
But to this the di fficulty w a sstarted that fissure s that
could let do w n w ater w ould pass up stea m The O h
je c tio n w h e n all th e conditions are ad e quately con
s
id e re d has really no w e ight ; and it has been com
p le te ly disposed of si n ce w ithin a fe w years it has b e en
proved that capillary infiltration goes o n in all porous
rocks to enor m ous d e pths and that the capillary pas
sages in such media though givi ng free vent to w ater
— and the m ore as th e w ater is w ar mer— are wh e n
once filled with liquid proof against the re turn through
the m o f gases o r vapours S O that the d e eply seated
w alls of the d ucts l e ading to th e crate r if of such
m aterial m ay be red hot and ye t continue to pass w ater
fro m e very pore (lik e the w alls o f a w ell in Chalk)
w hich isflush e d O ff into steam that cannot return by
th e w ay the w ater came do wn and must r each the
surface again if at all by the duct and crater over
comi ng in its w ay whatever obstructions they may be
fill e d w ith
And this re markabl e property o f c a pillarity s
fi
uf
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T H E LA T E E RUPTI ON O F V E SU V I U S
54
.
solid cr ust fractur e d into isolated frag ments by te nsions
due to its o w n contraction is supposed to sink into the
loats ; and much ing e nuity has
s
e a o f lava o n w hich it f
b e e n e x pe nded in imagining the m e chanis m by which
in plac e s the liquid m atter is supposed to rise a bo ve the
su rface o f the crust
I have no spac e for discussing these vi e w s further
than to asser t that in th e e xisting state o f our globe
a n d even ad mitting a solid crust of only
met res
thick dislocation of the c rust by tensio n is not possibl e
T he s
olid crust o f o ur globe as I hope w e shall see
furth e r o n is not in a state of tension and has not b een
so since i t w a sextrem e ly thi n a m er e p ellicle as c o m
pared w ith the liquid nucleus but is on the con trary
in a stat e of ta ng entia l co mp ressio n
H o w ever tenabl e in other r e spects may be the vol
th e o ry w hich rests upon the assumption O f a
c a nic
v e ry thin crust an d a u niversal oc e an o f fused rock
b e neath it fails wholly to explain m any o f the most
important circ u mstances observable as to the d istri
b u tio n and move ments o f existing Volcanoes on our
globe
It affords no adequate e xplanation of the configuration
of the lin e s o f Volcanoes no r o f their occurrenc e in
th e oc e an bed nor of their exist e nce in high latitudes
n e ar th e P oles Wh e re n o m atter h o w o r at w hat rat e
our glob e cooled from liquidity the crust must b e
thick e st ; nor Of the ind e pendenc e o f e ruptiv e action of
clos ely adj ac e nt volcanic v e nts nor of the non periodi
city the sudd e n aw akening u p to activity , th e as sudden
e xhaustion the long repose the gradual decay o f action
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I N TRO D U CTORY S KETC H
55
.
at particul a r vents and o f much more that might b e
stated and sustained as di fficulties left by that theory
unexplained or that are of a nature even Opposed
to it
The researches Of the last fe w years hav e ho w ever
as it app e ars to me rendered a ny th e o rv that d e mands
a sits postulat e s a v ery thin cr us
t and a universal liquid
nucleus beneath it absolutely untenabl e
Without attachi ng a ny i mportan ce to the arguments
o f Mr H opkins
based upon prec e ssion a nd nutatio n
it appears to m e o n various oth e r grounds som e o f
which have been urg e d by S ir Willia m Thompson
that the earth s solid crust is not a thin o ne at l e ast
no t thin e nough to render it conceivabl e that w ater
can e ve r gain admission to a fluid nucleus if any such
still e xist situated at so gre at a d e pth ; and w ithout
such acc e ss w e can h av e no Volcano It is not ne c e s
sary to go to the extent o f a crust o f 8 0 0 o r
mil e s
thick : w ith o ne o f half th e minor thickness I beli e v e it
may b e prov e d on various grou n ds hydraulic amongst
oth e rs that ne ither w ate r could r e ach th e nucl e us nor
th e liquid matt e r o f the nucl e us r e ach the surfac e
Mr H opkins havi ng prov e d to his o w n sati sfaction an
e normous thickness for the crust and s e ei n g cl e arly the
difficulties that this involv e d to the gene rally acc e pted
volcanic theory and having no oth e r to substitut e for
it fe ll b ack upon that most vague and w e ak notion of
the exist e nce o f isolate d lakes o f liquid rock existing
at comparatively small d e pths b e neath the e arth s surfac e
w ithi n the solid and r e lativ e ly cold crust each supplyi ng
its o wn Volcano o r more than o ne w ith ready made lava
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56
T
HE
A T E E RUPTI O N
or
L
V ES U V I U S
.
What is to produce thes e lakes Of fused mat ter in the
midst of si m ilar solidified matt e r ?what is perpetually to
m ai ntai n their fluidity in th e midst of solid m atter con
w hat ha sgi v en the m their loc al posi
tinu ally e o o ling
tion ?w hy near o r less n e ar the surface ?what should
have arranged them in dire ctions stretching in some
cas e s n e arly fro m P ole to P ol e
S u rely this creation o f imaginary lakes merely b e
cause it happens to fit th e vac ant chink that see ms
needed to w e d ge up a falli ng theory is an instance of
that abuse o f hypothesis against w hich N e wton so v ehe
”
Hyp o thesesno nfing o
me ntly d e clai ms
H ypothesis to be a philosophic scaffolding to kno w
l e d ge m ust as Whew ell h a ssai d be clos e to the facts
a nd no t merely co nnected w ith the m by arbitrary and
”
u ntried fa cts
! e t this appears accepted by Lyell
1
0
h
e dition
ol
2
2
e lse wh e re ; by
V
p
and
t
7
)
(
”
P hillips
Vesuvius pp 3 3 1
by S crope if a s
”
I hop e I mistak e him no t
Volcano e s pp 265
3 07
tho ugh none o f these excellent authoriti e s
seem e ither quite clear or quite satisfied with the notion ;
and i n the very passage referred to L yell may have
possibly a much more philosophic notion in vie w where
h e says :
It is only ne cessary in or d er to explain the
action o f Volcanoes to d iscover some ca use which is
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f
suc h
f hea t a s
may me lt o ne after the o ther certa in p o rtio nsof the s
o lid
t so as to for m s e as lakes or oceans o f subterra
cr us
”
ne ons l a va
o l II
pp
226
If
by
this
is
V
(
me ant that all that is n e e ded to co mplete a true theory
of volcanic action is to discover a n a d eq ua te c osmica l
p a ble
ca
o
bring ing
a bo ut
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a co ncentra tio n o
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I N TR O D U CT O RY S KETC H
ca us
e
57
.
that is to say a pri me mover to which
f
all its pheno m ena m a
y be traced back w hich shall be
at O nce reconcilable w ith the conditions o f o u r plan e t
as a cooling m ass in space and w ith facts Of Vulcan
ology as they are no w seen u pon it— then I entirely
a gree w ith it
It has been my o wn obj ect to endeavou r to discover
and develop e that adequate cause in a P aper O n Vol
c a nic E n e rgy an A ttempt to d e v e lop e its Tru e N ature
and Cosmical R elations read (in abstract ) befor e th e
R oyal S ociety of L ondon P roceedings R oyal S ociety
Vol XX Ma y
and no w (O ctober 1 87 2 ) under
consid e ration o f Council w ith a V ie w to publicatio n
I propose concluding this revi e w of th e progress o f
Vulcanology (in w hich I have had to limit mys elf to
revie w i ng merely the chie f stages o f advance to w ards
kno wl e dg e of the nature and origin o f volcanic heat
its e lf and have had to pass w ithout notice the vast and
imp o rtant m ass Of facts and reasonings collected by so
many laboure rs as to its visibl e ph e nomena and pro
d ucts and the still gr e ate r m ass o f sp e culation good
and bad on e very branch o f the subj e ct) by giving a
n e cessarily very bri e f and i mp e rfe ct sk e tch of my o wn
It w ill first
v ie w s as in that P aper in part developed
be necessa ry to retrac e our steps a littl e in ord e r to
gain such a point as shall afford us a fuller vi e w o f the
w h ol e probl e m b e fore us
It is not necessary to dilate even did space allo w
u pon the m any points w hich bind tog e th e r E arth q uak e s
and Volcanoes as b e lo nging to th e play of like forc e s
T hese are generall yadmitted ; and in v a rious w ays m or e
the hea t—
or
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T H E LA T E E RU P TIO N
58
0 F
VESU VI U S
.
or les sobscur e geologists generally have supposed some
relations b e tw e e n th e se and the forces o f e levation
w hich hav e r aised up mo untain chains etc
N o o ne ho wever that I a m aw ar e of prior to m ys e lf
in the P aper j ust all ud e d to has atte mpted to Sho w
still l e ss to prov e upon an e xp e rimental basis that all
of volcanic action and
the phenomena o f e l e vation
o f E arthquak e s are e xplicable as parts o f one simple
machi ne ry— nam e ly the play o f forces resul ti ng from
the secula r cooli ng of o u r globe
We have seen that
o n th e w hol e both E arthquakes and Volcanoes follo w
along the great lines of elevation o f o u r surfac e A ny
true solution O f the play o f forc e s w hich has p rod uced
any o ne o f those thr e e classes o f pheno men a must
connect itself w ith th e m all and be ad e quate to account
fo r all
A nd this w ould hav e earlier been s e e n ha d
geologists g e nerally framed for themselves any corr e ct
notions of the m e chanis m o f el e vation itself and s ee n
its real relation w ith the s e cular cooling of o ur pl anet
But the play of forces resulting from this se cular cooling
has n e v e r un til very r e c e ntly been adequately o r tr uly
stat e d T he arbitrary a ssumption and n e gl e ct of s e v e ral
essential cond itions b y L a P lace in his c el e brat e d P ap e r
O n the Cooling o fthe E arth in the fifth volum e of the
M é caniqu e Celeste and the arbitrary and unsustainable
h v p o the s
isof P oisson upon the same subj ect have tended
to r e tard the progress of physical G eology as to the nature
o fe levation : the first by leavi ng the g e ologist in doubt as
to w h e th e r our globe w e re cooling at all ; the second by
sugg e sting distorted n otions as to the mo d e of its cooling
and consolidation O n the other hand neither geologists
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I N TRO D U CTORY S K E TC H
59
.
nor mathe m aticians generally have framed for the m
selv e s any Clear notions Of the m e chanis m of elevation
H ad a true conception been for med o f the forc e s and
interior movements brought necessarily into Operation
by the secular cooling o f the glob e g e olog ists could
scarcely have failed to see that th e ir notion as to the
w a y and dir e ction i n w hich the forces producing el e va
tion have actually acted could not if arisi ng fro m
refrigeration be those w hich th e y have almost univer
s ally supposed nam ely — some force acting v erticallv u p
w ards i e radially from the centre Of th e sph e re
H ad
geologists only looked at N atur e w ith Op e n e ye th e y
m ust have s e en that m ountain rang e s a nd e levations
generally (exclusive Of volcanic con e s ) pr e sente d c ir
c um s
ta nc e s absolut e ly incompati b le w ith thei r having
b e en thrust up by any force p rima rily acti ng in the
direction Of a radius to the spheroid
! e t this is the e rron e ous notion o f the mechanis m of
e levation w hich to the present hou r pr e vails amo ngs t
geol o gists so far as th e y in gen e ral have fram e d to
th e ms e lv e s any distinct id e a Of such m e chanism at all
Thus only to cite tw o exampl e s fro m r e c e nt authors
L y e ll says Of th e proba
o f j ustly high reputation
ble subterran e an sourc e s w heth e r o f up ward or do wn
w ard move ment w hen p e rmanently uplifting a country
and in reference to the crumpling Of strata o n moun
tain fl anks b y lat e ral pressure it w ould be rash to
assume th e s e able to resist a po wer Of such stup e ndous
en e rgy if itsd irectio n instea d of being v ertica l happen e d
”
to be oblique or hori z ontal T his is some what vagu e
and I trust I do not mis take o r misrepresent the illustrious
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T H E L AT E E RUPTI O N
60
0F
V ES U V I U S
.
author yet it is the m ost e xplicit expression I can find
in the P rinciple sof G eol o gy as to his notion o f the
pri m ary direction o f e l e vato ry force (E dit 1 0 Vol
p
That Mr S crop e s id e a is that only o f primary
radial or vertical direction O f such forces is a pparent o n
”
inspe cting his D iagram N O 64
V olcanoes
p
and in the use Of the w ords
an axial w edg e of
”
g ranit e which o n the n e xt page w e find is liqu e fied
granite
and if w e read on to page 2 9 4 and r e fer also
to pag e s 5 0 and 5 1 I b eli e v e there can be no doubt that
t is the author s notion Of the
v er tica l or d irec t up thr us
primary direction Of all forces o f elevation The true
nature of these forces w a s ho w ever clearly seen and
Compt
most j ustly stated by Constant P revost
To me XXXI 1 8 5 0 and Bulletin de la S oci é té
B e nd
”
1 84 0 ) as consisting not
Tom e
G é o lo g de France
in forces o f so me unkno w n origin acti ng primarily ia
sures a cting hm
th e vertical but in ta ng entia l p res
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by mu tua l p res
o lv ed
s
ures a t
y, a nd res
u lta nts
t
t
These P revost
i
n
s
i
n
o vertica l res
o
p
z o nta ll
cer ta in
rightly
attributed to the contraction o f the earth s solid cr ust
T he sa me idea has be e n adopted by Elie de B e aumont
as th e true m echanism o f the elevation O f mountain
rang e s ; and although D e Beau mont s vie ws as to the
thinn e ss he assigns to the solid and contracti ng crust
ange deduction as to the parallelis m o f con
a nd hisstr
te mporaneous m ountain chains uplifted by its spas
modic a ction along ce rtain lin e s may be untenable his
the play of forces producing
notion g enerally as to
m ountain elev a tion is much more nearly correct
Mr H opkins s notion is S imply that o f the geologists
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T H E LA T E E RU PTI ON O F V E SU V I US
62
.
gradually conve rt e d into ta ng entia l p ressures the con
t raction O f the nucl e us no w beginning to e xceed (for
equal loss e s of h e at) that o f th e crust through w hich
it cool e d A t this st ag e th e s e tang e ntial pressures gave
ris e to the chief e levations of m ountain chains — not
by liquid matter by any process bei ng i nj ecte d from
b e ne ath v e rtically but by such pressures mutually
r e acting along c e rtain lin e s b ei ng res o l ved i nto the
v e rtical and forcing up w ard smore or less of the crust
itself The gr e a t outlin e s of th e mount a in rang e s and
the gre ater el e vation of the land w e re designated and
formed du ri ng th e long p e riods that e laps e d in
w hich th e continually increasing thickness of crust
remain e d such that it w a s still a s a w hol e fle xi bl e
e nough o r opposed su f
fici e ntly little r e sis tanc e to crushing
to admit of this u pris e o f mountain chai ns by resolv e d
tangential pressur e s
I hav e sho w n that the si mpl e
m e chanism of such tang e nti a l pr e ssur e s is co mpetent to
a ccount for a ll the compl e x ph e nom e na both of the
e l e vations a nd Of the d e r es
s
io nsthat w e no w see on the
p
earth s surface (oth e r than contine n ts and ocean beds)
including the production Of gaping fissures (in directions
g e n e rally orthogonal to those of tangential pressure )
A nd as our e arth is still a cooli ng body and the crust
ho w ever no w thick e r and m ore rigid is still incapabl e of
sustaini ng the tangen tial pr e ssures to which it is no w
exposed so I by no me ans infe r tha t slo w and s mall
(r elativ ely ) movements o f elevation and d e pression may
not be still a nd no w going o n upon the earth s surface
in fact all th e ph e nomena o f e l e vation and d e pressio n
r e ndi ng etc w hich at a much remoter e poch acted
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I N TRO D U CTORY S KETC H
63
.
upon a much grander and m ore effe ctiv e scal e S o that
for au ght my v ie ws say to the contrary all the m ount ain
chains in the w orld m ay b e possibly increasing in statur e
year by year o r at times ; but in any cas e at a rat e
imally small in its totality over th e w hole
almost infinite s
e a rth to that w ith which their ridges w ere originally
u preared
But the thickness of the earth s crust — thus constantly
add e d to by accretion o f solidifyi ng m a tte r from the
still liquid or pasty nucl e us as th e w hole m ass h a s
coole d— has no w assum e d such a thickness as to b e abl e
to o ffer a too considerable r e sistance to th e tangential
pressures to admit o f its giving w ay to any large e xtent
by r e solution u p w ards ; ye t th e cooli ng of the w hol e
m ass is goi ng o n and contraction th ough unequ al both
o f thick
crust and of hott e r nucl e us ben e ath also
w hether the latt e r be no w liquid or not
W e re the c o n
traction lineal o r cubical for e qu al d e crem e nts or lo ss e s
o f h e at or in equal tim e s — e qual both in th e m at e rial
of the solidified crus t and in that of the hotter nucl e us
th e r e could be no such tang e ntial pr e ssures as are h e re
referred to at any e poch of the earth s cooling
But in
accordance w ith the facts of e xperimental physics w e
kno w that the c o e fficie nt Of contraction for all bo d i e s
is gre ater as their actual temp e ratur e is higher a nd this
both in their solid and liquid states
H ence for equal d e cre ments Of hea t o r by the coolin g
in e qual times , the hott e r nucleus contracts more than
does its envelope o f solid matt e r
The result is no w as at all periods since the signs
changed of the tangential forces thus broug ht into play
— tha t th e
i e since they became tangenti al p res
sures
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,
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64
LA T E E R U P TIO N
T HE
VES U VI U S
0F
.
ucleus tends to shrink aw ay as it w ere fro m beneath
th e crust and to leav e th e latter unsupport e d o r but
par tially supported as a sph e roidal dome above it
N o w what happens ? I f the hollo w sphe roidal shell
w er e strong enough to sustai n as a Spheric dome the
t a ng e nti al thrust Of its o w n w ei g ht and the attraction
of the nucleus the sh e ll w ould be left behind altoge ther
by the nucleus and th e latt e r might be conceived as a n
ind e pendent globe revolving centrally or ex ce ntrically
w ithin a shell outsi d e o f it
This how ever is no t w hat
h appens
The question then arises Can the solid shell suppor t
the tangential thrust to w hich it w ould be thus exposed ?
By the application to this proble m of an elegant theore m
O f L agrange I have proved that it canno t possibly do
so no matter w hat may be its thickness no r w hat its
m aterial even w ere w e to assu m e the latter n o t mer e ly
Of the hardest and most resistant rocks w e know a ny
thing o f but even w ere it o f te mpered cast steel the
most resistant substance (unless possibly iridio osmiu m
L agrange
e x ce e d it) that we kno w anything about
h a ssho w n that if P b e the nor m al pressure upon any
fl e xible plate curved in both directions the radii o f these
”
p rincipal curvatures bei ng 3 a nd g and T the tang e n
tial thrust at the point o f ap plication and due to the
forc e P then
n
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,
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,
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,
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,
‘
-
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'
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,
’
,
,
P
T
L
1
7
+
6
When the surfa ce is spherical
such
’
,
g
”
g
,
or
ma y
and
P
'
g
2
be viewed as
I N TRO D U C TORY S KET C H
65
.
P is for a unit square (take n
assu med as plane) O f the shell
u p po s
e a square m ile
e qual to the e f
fect o f gravity
I pon that unit g b e ing th e earth s ra d ius and if w e
u me the unit square be also a unit in thickness
s
Is
9
is then the w eight o f a cubic mil e O f its m aterial ;
roughly) the e arth s radius as
Ind if w e take (
niles the tangential pre ssure T is o n ea ch fa ce o f the
zubic mile equal to
In the
present case
ela tiv ely s m all and S O
,
,
’
,
,
,
’
,
,
,
,
,
4 000
P
2
,
equal to the pressure o f a column O f the same m aterial
of
ti mes its w eight
If the cubic mile that w e hav e thus supposed cut
o u t o f the earth s crust at the surface w ere Of th e
hardest kno wn granit e o r porphyry it w ould be exposed
to a crushi ng tang e ntial pressure equal to bet ween
4 0 0 and 5 0 0 ti me s w hat it could w ithstand and so m ust
crush even though o nly l e ft unsupported by the nucleus
beneath to the e x t e nt o f
or 3 1
O f its entire
And w hat is true h e re o f a mile taken at the
w eight
s u rface is true (ne gle cti ng som e minute corrections for
di fference in the c o effic ient o f gravity etc ) if taken at
any other depth w ithin the thick cru stfi“
31
‘
.
’
,
,
,
,
0
,
.
,
-
.
,
ev
.
0
.
r,
r
r
F
O
ish e
MA
a m ost inte e sting and
valuable Pape
n th
E l vatio n f M ountai n Chains by Late al
P essu e its Cause a nd th A m ou n t f it w ith a S peculation o n the
ad A p il 1 868 and publish ed in th
O rig in o f V olcani c A ction
T ansactions o f th Camb idg Philosophical S ocie ty V ol ! I
P a t III in 1 8 69 has d duc d th n ec ssa y c ushing o f the e arth s
c ust by a diffe e nt but clos ly analogous method I had no t se n
this Pap e u ntil aft er my w n w sin th hands o f the R oyal S oci ty
n t f om my o w n and do no t
w holly diff
T h author s volcanic vi w s
appe a to me eq ually valid w ith his n otions as to e le vatio n — R M
T he R
r,
e
re
.
,
r
e
,
e
r
,
r
e
o
e
e
,
,
e
e
r
.
.
,
,
’
r
e
r
’
,
e
r
r
r
o
o
”
e
r
in
,
e
,
r
.
e
,
,
.
e
.
e
a
er e
a re
r
e
r
,
.
F
.
.
T H E LAT E E RUPTI ON O F V E SU V I U S
66
.
The crust o f our e arth th en as it no w is must crush
to follow down after the shrinking nucleus— if so b e
that the glob e be still cooling and constituted as it is ;
e v e n to the limited extent to w hi c h we know anything
o f its nature — it m ust crush uneq u ally both regarded
superficially and as to depth ; generally the crushing
lines being confined to the planes or places of greatest
w eakness ; and th e crushing will not b e absol u tely con
s
tant and uni form any w here or at any time o r at any
of tho se places of weakness to which it will be princi
pally confined but will b e more o r less irregular quasi
or
paroxysmal : as is indeed the way in
p e rio clic
more o r less rigid)
w hich all known m aterial subst a nces (
give w a y to a slo w and constantly increasing steady
pressure
W e have now to ask Ho w mu ch o f this crushing is
going on at present year by year T A nd the answer to this
depends u pon w hat am ount of heat o ur W orld is losi ng
into space year by year
Geologistswho have taken o n trust the statement
that La P lace has proved that the world has lost no
sensible amount o f heat for the last
years seem
generally to suppose that to be a fact ; but in reality La
P lace has p ro ved nothing of the sort as those geological
teachers w h o have echoed the conclusion should have
known had they deciphered the mathematical argu
m ent upon which it has been supposed to rest
By application o f Fourier s theorem (o r definition ) to
the observed rate o f increment of heat in descendi ng
fro m the geoth ermal co uche of invariable temperat ure
and the c c e fficientsof conductivity of the rocks of our
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I N T RO D U C T O R! S K ET C H
67
.
earth s crust as given by the long contin ued observa
tions made beneath the O bservatories o f P aris and o f
E dinburgh it results that the annual loss o f heat into
space of our globe at present is equal to that which
would liquefy into water at 3 2 Fahr about 777 c ubic
miles of ice ; and this is the measuring unit for the
amount o f contraction of our globe no w g oing o n
The figures are not probably exact fo r the data are not
ficiently full or exactly established as yet ;
o n a basis su f
b u t they are not very widely wrong and thei r precise e x
a c tne s
sis not material here N ow h o w is this annual loss
e may please to V iew it
o f heat
great
or
small
as
w
)
(
fro m the interior of our globe disposed o f!
What does it d o in the interior 7 We have already
seen that it is primarily disposed o f by conversion into
w ork ; into the work of diminishing the earth s volume
as a Whole and in so doing crushing portions of the
solid surrounding shell
B ut does the transformation o f lost heat into the
work of vertical descent and of the crud i as it follow s
down after the shrinking nucleus end the cycle ? N o
A very large portion o f the mechanical w ork thus pro
d u c e d and resolved as we have seen into tangential
crushing pressure is retransformed into heat again in the
If
v ery act of crushing the solid material o f the shell
we see a cartload o f g ranite p aving stones shot o ut in the
dark we see fire a nd light produced by their collision if
we rub two pieces o f quartz together and crush thus
their surfaces against each other we find we heat the
pieces and evolve l ight
The machinery u sed for crushing by stea m power
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F
2
68
T HE
LA T E E RUP TI O N
or
V E SU V I U S
.
hard rocks into road metal gets so hot that the surfaces
cannot be touched
These are familiar instances of one result o f what is
no w taking place by the cr u shing of the rocky masses
of our cooling and descending earth s crust every hour
beneath our feet only upon a vastly greater scale It
is in this local transformation o f w ork into heat that
I find the true origin o f volcanic heat within our globe
But if we are to test this so as in the only way possible
to decide is it a true solution o f this great problem
we must again ask the question H o w much ? and to
answer this we m ust determine exp erimenta lly how
m u ch heat can be developed by the crushing of a give n
v olu m e say a cubic mile of such rocky materials as W e
know must constitute the crust of o ur globe down
to the botto m of the kno w n sedimentary strata and
extendi ng to such crystalloid rocks as we may presume
underlie these W e must also obtain at least a ppro xi
m ately what are the c c e f
fic ie nts of to ta l co ntra ctio n
between fusion and atmospheric temperature of such
m elted rocks basic and acid silicates as may be deemed
representative o f that c o e ffic ient fo r the range o f vol
cani o fused products basalts trachytes etc whic h
probably su fli cie ntly nearly coincide with that of the
w hole non metallic m ass of our globe
The first I have deter mined experimentally by two
d i fferent methods but principally by the direct o ne of
the w o rk expended in cr u shing prisms of sixteen re pre
s
e nta tiv e
classes of rock ; the specific gravities and
s
pecific heats o f w hich I have also determined
If H be the height of a pris m of rock crushed to
powder by a pressure P applied to two opposite faces
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T H E LA T E E RU P TI O N
70
VES UVI U S
0 F
.
that each cubic m ile o f the mean m aterial o f such
a crust wh en cr u shed to powder developes sufficient
heat to melt
cubic miles of ice into water a t 3 2
cubic miles of water from 3 2 to 2 1 2
o r to raise
Fahr o r to boil o ff 1 1 24 cubic miles of water at 3 2
into steam o f one atmosphere o r taking the average
F ahr to melt
melti ng point o f rocky mixtures at
nearly three and a half cubic m iles O f such rock if of
the same specific heat
O f the heat ann u ally lost by our globe and dissipated
into space represented by 7 7 7 cubic miles of ice m elted
as before stated the chief part is derived fro m the actual
hypogeal source of a hotter though not necessarily fused
nucleus and nearly if not wholly is quite independent
of the heat of Vulcanicity which is developed as a con
sequence O f its loss or dissipation But were we to take
the extreme case and suppose it possible that all the
heat the globe loses annually resulted from the trans
for m ation o f the work of internal crushing of its shell
we shall find that the total volume o f rock needed to
be cr u shed in order to produce the required amount of
lost heat is perfectly insignificant as compared with the
volume of the globe itself or that of its shell For
as 1 2 7 0 c u bic miles of crushed rock developes heat
equivalent to that required to melt o ne cubic mile o f ice
to water at
and if we assume the volum e o f our
globe s so lid cr u st to equal o ne fourth o f the total
vol u m e of the entire globe 9 87 cubic miles o f rock
cr u shed annually would supply the whole o f the heat
d is
s
ipated in that time But that is less than the o ne
six ty—five millio nth o f the volum e of the crust o nly
B ut a very sm all portion of the total heat annually
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°
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°
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°
°
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I N T R OD U C T O R! S K ET C H
71
.
lost by o ur globe is suffi cient to account for the whole
of the volcanic energy o f every sort including thermal
waters manifested annually upon o ur earth In the
absence of com plete data we can only approximately
calculate what is the annual amount o f present volcanic
energy o f o ur planet This energy shows itself to us
in three ways : 1 The heating o r fu sing of the ej ecte d
solid m atters at volcanic vents 2 The evolution of
steam and other heated elastic fluids by which these
are carried 3 The work of raising through a certain
height all the materials ej ected T o which we must add
a large allowance for waste o r thermal mechanical and
chemical energy ine ffectually dissipated in and above
the ven ts A ll these are measurable into units of heat
I have applied this m ethod of calculation to test the
adequacy o f the source I have assigned for volcanic
heat in tw o ways viz : 1 To the phenomena presented
during the last two thousand years by Vesuv ius the
best known V olcano in the world ; and 2 T o the
whole o f the four hun d red and Odd volcanic cones
observed so far upon o ur globe o f which not more than
o n e half have ever been known 1 n activity
It is impossible here to refer to the details of the
method o r steps Of these calculations The result how
ever is that m aking large allowances for presumably
defective data less tha n o ne fo urth o f the total tellu ric
heat annually dissipated (as already stated in amo u nt)
is sufficient to account fo r the annual volcanic energy at
present e x pended by o ur globe
It is thus represented by the transformation into heat
mean )
o f the work o f crushing about 2 4 7 cubic miles of (
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T H E LA T E E RU P TI O N
72
0 F
V E SU V I U S
.
rock a quantity so perfectly insignificant a s compared
with the volume of the globe itself as to be absolutely
inappreciable in any way but by calculation ; and as
its mechanical result is only the vertical transpositio n
transitorily of material w ithin o r upon o u r globe the
proportion of the m ass of which to the whole is equally
insignificant so not likely in any way to produce changes
recognisable by the astronomer
S pace here forbids my entering at all upon that
branch o f m y investigation which is based upon the
experimental results above mentioned of the total con
traction o f fu sed rocks : for these the original P aper can
I hope be hereafter referred to I am enabled however
to prove thus how enormously more tha n needful has
been the store o f energy dissipated since our globe was
wholly a m elted mass for the production through the
contraction of its volume of all the phenomena of
elevation and of V ulcanicity w hich its surface presents
A nd h o w very small is the am ount of that energy in a
u nit o f ti m e as no w Operative when co m pared with the
same at very re m ote epochs in our planet s history
I have said that if we can find a true cause in N ature
for th e origi nation of volcanic hea t all the other known
phenomena at and about volcanic vents beco m e simple
L avas and all other solid ej ecta of Volcanoes fro m all
parts of the earth s surface as w ell as basalts present
in chemical and physical constitution close resemblance
and may be all referred to the m elting O f more o r less
fusible m ixtures of siliceous crystalloid rocks with alu
m inous (slates etc ) and calcareous rocks Their general
che mical composition and the higher o r lower tempera
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I N T R OD U C T O R! S K ET C H
73
.
tures of fusio n resulting therefrom together with the
higher or lower temperatures to which they have been
submitted at the di fferent volcanic foci determine their
di fference o f flow (under like surface conditions ) and of
mineral character after ej ection and cooling
S t Clair de Ville and Fouqu e have sho w n that the
gaseous ej ections of which stea m forms probably 9 9
per cent are such as arise from water admitted to a p re
,
,
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.
,
.
,
fo cusof hig h temp era ture
Whether sea or fresh water is not material when w e
bear in mind that the chemical constituents found in sea
water and in natural fresh waters that have penetrated
the soil are on the whole alike in kind and only di ffer
in proportions But I must pass almost without notice
all the varied and instructive phenomena w hich are pre
sented by volcanic vents for to treat of these at all would
be to more than double the size of this sketch
In the source that has been pointed o u t as that from
which v olcanic heat itself is derived viz the secular
co o ling of o u r globe and the e ffects of that u pon its solid
sh ell we are enabled to p o int to that which is the sure st
test of the truth of any t heory— that it not only enable s
us to account for all the phenomena near o r remote
but to predict them We see here linked together as
parts of one grand play of forces those of contraction by
cooling producing by d irec t mechan ical action the ele
vation o f mountain chains and by their ind irect action
by transformation of mechanical work into heat the pro
duction o f Volcanoes ; and both by direct and by indirect
action o f E arthquakes never previously sho w n to have
thus the ph ysical connection o f o ne common cause
ex is
tent
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T H E LA T E E RU PTI O N
74
O F
V
E SU V I U S
.
but merely supposed more o r less to be conne c ted by
their distribution upon our earth s surface
We no w d iscern thus the physical cause why Volcanoes
are d istrib u te d viewed largely linearly and follow the
lines of elevation ; we see equally why their action is
uncertain non periodic fluctuating in intensity with
l o nger o r shorter periods o f repose shifting in position
becoming extinct here appearing in ne w activity or for
the first time there
We have an adequate sol ution
o f the
before inexplicable fact o f their propinquity
and yet want o f connection
We have an adequate
cause for the fusion o f rock at local points without re
sorting to the baseless hypothesis of perenni al lakes of
lava etc
F o r the first time to o we discern a true physical cause
for earthquake movement where volcanic energy does not
s
how itself The crushing of the world s solid shell
w hether thick o r thin goes on p er s
a ltnm and at e v er
s
hifting places however steadily the tangential pressure s
producing i t m ay act H enc e crushing a lo ne may be
shown to develope amply sufficient impulse to produce
the most violent E ar thquakes whether they be o r be not
at a given place or time connected with v olcanic out
burst or possible inj ection or with tangential pressures
enough still in some cases to produce partial permanent
ele v atio n
When subterraneous crushing takes place and the
circumstances o f the site do not permit the access of
water there m a y b e E arthquake but can be no Vol
cano ; w here water is admitted there may be both
A nd thus we discern why there are comparatively fe w
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I N T R OD U CTO R! S KE TC H
75
.
submarine Volcanoes the floor of the ocean being o n
the whole water tight
puddled
as an engineer
would say by the huge deposi t of incoherent mud etc
that covers most of it and probab ly having a thicker
crust beneath it than beneath the land
We see moreover that the geological doctrine o f
absolute uniformity cannot be true as to Vulcanicity
any more than it can for any other energy in play in
o u r world
Its development was greatest at its earliest
stages when the great masses o f the m ountain chains
were elevated It is even now— though as co m pared to
m en s experience and even to all historic time apparently
uniform a nd always the same — a decaying energy
The regimen o f o ur planet as part of the Cosmos
w hich seems to some absolute (
and presented to P layfair
n o trace of a beginning nor indication o f an end ) is not
absolute and o nly seems to us to be so because we see
so little of it and of its long perspective in time This
th e no w established doctrine of th e conser v ation o f
energy renders certain
With this source for volcanic heat too in our posses
sion we can look from our o w n world to Oth ers a nd
predict within cer tain limits which must widen as o u r
knowledge o f the facts of their substance and surface
becomes greater what have been and what are the
developments o f V ulcanicity w hich have taken place o r
are occurring in o r upon them Looking to our o w n
satellite we see fo r the first ti m e a sufficient physical
cause for the enormous display o f volcanic energy there
which the telescope d ivulges to us ; o ne w hich is no t to
be explained alone by the commonly made statement o f
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T H E LA T E E RU P TI ON O F V E SU V I U S
76
.
the small density of the moon b u t by the fact that as
the rate of her cooling from a given temperature as
compared w ith that of our earth (apart from questions
o f the chemical nature of the two bodies or of their
specific heats
has been inversely as their respective
ses and directly as their surfaces so has the rate O f
m as
cooling Of the moon been vastly greater than that of the
earth and the energy due to contraction by cooling
more intense and rapidly developed in our satellite than
u pon our globe
We have thus traced in meagre and broken outline
only— because space adm itted no more — the progress of
S cience to its existing state as respects Vulcanicity in
its tw o branches of Vulcanology and o f S eis mology
and pointed o u t their more intimate relations and points
o f connectio n a nd been at length able to refer the m on
the sure basis of physical laws to one co m mon cause
and that o ne derived fro m no hypothesis but simply
from the postulate of our world as a terr aqueous globe
cooli ng in space
What I have here advanced with reference to volcanic
energy w hich appertains to m y own researches I do
not conceal from myself nor from the reader has yet to
await the reception generally and the aw ard o f the true
men o f science of the world
That like every ne w line of thought which has
atte m pted or succeeded in supplanting the O ld it will
m eet with Op position I make no doubt
My belief however is that in the end it will be
found to have added a frag ment to the edifice of true
knowledge
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T H E LAT E
78
E arthquake
E
RUP TI ON
V E SU V I U S
or
.
the Volcano is not destructive but pre
But we now see that : that the preservative
s
e rv a tiv e
sc o pe of this function as respects o ur earth is far w ider
than w hat has been previously attributed to it T he
Volcano does not merely thro w up new fertile soil and
tend in some small degree to restore to the dry land the
w aste for ever going o n by rain and sea ; it fulfils a far
weightier and more imperative task ; it— b y a mecha
nism the power o f which is ex actly balanced to the
v ariable calls demanded o f it and which working al m ost
i m perceptibly although in a m anner however terrible its
s u rface action may at times appear to us li ttle men *
prevents at longer intervals such sudden and unlooked
for paro x ysms in the mass o f our subsiding earth s shell
a s would be attended with wide spread destruction to
all that it inhabi t
To the popular mind Volcanoes and E arthquakes are
only isolated items of curiosity amongst the wonders
few geologists even appear to realise ho w
o f the world :
great and important are the relation so f Vulcanicity to
their science viewed as a whole ! e t o f Vulcanicity it
is not to o much to say that in proportion as its nature
and doctrines come to be known and understood as parts
of the Cosmos the nearer will it be seen to lie at the
basis o f all P hysical Geology
a nd
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Magna ist q
a
u ia
parv i s mus
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u
E N D
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S E N E CA,
-
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! uaas N a t
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”
PR O F E SS O
R
E R U P T IO N
P AL M I E R
I
’
ACCO U N T
T
T HE
OF
E R U PT IO N
.
great and disastrous co nflag ra tio n o f V esuvius
which took place on the 2 6th o f A pril 1 872 was in my
opi n i on the last phase of an eruption which commenced
at the end o f J anuar y 1 8 7 1 an account of which I was
unwilling to w rite because I was convinced that it
would no t really terminate without a more o r less violent
e x plosion such as I had often predicted I shall no w
state the reasons u po n whic h my prediction was
foun d ed
W hen the central crater begins to heave with slight
eruptions o ne m ay al w ays predict a series o f slight co n
v ul sions o f greater o r less duration
which are pre
paratory to the grand explosion after which the Volcano
remains fo r the most part in repose
Thus whe n
I Observed the cone fissuring in N ovember 1 8 68 and
s
u l ng from it and flowing over
0 0 pious lava streams I s
the beautiful and fertile plains of the N ovelle through
the Foss a della V e tra na instead o f announcing the
beginning o f an eruption I announced the termination
o f one which had been mani fest for upwards o f a ye a r
by the constant flo w o f lava from the summit of the
co ne
From the month of N ovember 1 868 until the end o f
HE
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82
T
HE
LA T E E RU PT I ON O F V E SU V I U S
.
D ecember 1 8 70 the mountain remained quiet except
that the fumaroles at the head of the fissure showed
a degree of activity by w hich chlorides and sulphides of
C opper sulphide of potash and other products w ere
e ngendered
But in the beg inning o f 1 8 7 1 the seismograph w a s
d isturbed (1 ) and the crater dischar g ed with a slight
detonation a few incandescent proj ectiles Then I an
whic h
no u n c e d that a new e rup tio n ha d co mmenced
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mig ht be
es tha t
lo ng d ura tio n, b ut w ith p ha s
co u ld
f
and o n the 1 3 th J anuary on th e
sibly he fo reseen
p os
northern edge o f the u pper plain of the Vesuvian cone
an aperture a ppeared from w hich at first a little lava
issued and then a small cone arose and threw o ut
incandescent proj ectiles with much smoke of a reddish
colour whilst th e central crater continued to detonate
more loudly and frequently The lava flo w continued
to increase u ntil the beginning o f March w ithout
extendi ng much beyond the base of the cone although
it had great mobility
In March this little cone
appeared not only to subside but even partly to give
Way as almost happens with eccentric cones when their
activity is at an end U pon visiting it I observed th a t
fo u r pris m atic o r pillar —like masses remained standing
three of which were formed o f scori ae which had fallen
back again in a pasty conditio n and had become
soldered together th e fourth consisting o f a pyramidal
block of compact and lithoidal lava w hich appeared to
h ave been forced u p by impetus fro m the ground
beneath A little s m oke iss ued from the s mall crater
and a loud hissing from the interior was audible
o
no t
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V
E SU V I U S EA R LY I N 1 87 1
83
.
By lying along the edge I could see a cavity of
cylindrical for m about ten metres in depth tapestried
with stalactitic scori ae covered with sublimations o f
various colours The bottom o f this crate r was l e vel
but in the centre a small cone o f about two metres ha d
formed pointed in such a manner that it possessed but
a very narrow openi ng at the ape x from which smoke
issued with a hissing soun d and from which were
spurted a fe w very small incandescent scori ae Thi s
little cone increased in size as well as activity until it
filled the crater and rose four o r five metres above the
brim * N e w and more abundant lavas appeared near
the base of this cone and pou ring continually into the
A tria del Cavallo rushed into the Fossa della
V e trana in the direction o f the O bservatory and
towards the Cro cella where they accumulated to
such an extent as to cover the hill side for a
distance o f about 3 0 0 metres ; then turning below the
Cantero ni they formed a hillock there without spread
ing much farther These very leucitic lavas are capable
o f great e x tension the pieces which are ej ected forming
fo r the most par t very fine filifo rm masses which may
be collected o n the mountain in great quant ities and
specimens of which I presented to the A cademy unde r
the name o ffilifo rm lap illi These threads were often
of a clear yellowish colou r and when observed under
the microscope were found to consist o f very minute
crystals o f leucite embedd ed in a homogeneous paste
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t A p ril , isd es
crib e d a n d
ma ll c o ne, a sit a p pea re d o n the 1 s
T hiss
dra wn in a Me m o ir o f P ro fe sso r v o n B ath, o f the U niv ersity o f B o nn,
t a nd 1 7th o f A p ril ,
uv iuso n th e l s
V es
On
9‘
G
2
T H E LATE E RUPTI ON
84
V
0F
E SU VI U S
.
The crystals were still smaller as the diameter of the
threads was less and never formed knots o r swelling s
even in the most hair like threads These observation s
le d me to rej ect th e Opinion of those who hold that
crystals o f leucite are pre existent in the lava The
viscous nature o f these lavas prevented their being
covered with fragmentary sc o rim but caused the forma
tion at first o f a skin which thickeni ng became at last
a more o r less pliable shell that when more solidified
a llowed the still fluid part to run as in a tube formed
o f this solid shell
For many months the lava descended
thus from the cone and traversed the A tria d el Cavallo
always covered appearing below the Cantero ni o f a
lively fluidity until it could no longer be enveloped in
its skin which was stretched by the addition of ne w
lava and finally rent asunder to give room to the cur
ren t until owing to d iminished liquidity it was c o n
strained to stop When the lava having traversed the
covered channel it had made for itself from the top o f
the mounta in to below the Cantero ni made its appear
ance s till running it frequently formed large bubbles
o n the s u rface w hich mostly burst to give vent to s m oke
and then disappeared
In O ctober 1 8 7 1 near the e d ge o f the central crate r
another small crater w a s formed by falling in which
after a fe w days gave vent to smoke and several j ets
o f lava
The pri ncipal cone fre quently Opened in some
point o f the slope to give eg ress to small currents o f
lava which quickly cease d But towards the end o f
O ctober the detonations increase d the smoke from the
central crater issued more densely and mixed with
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T H E LA T E E RU PTI ON
86
V E SU V I US
0 F
.
metre s and the central crater a ne w crater o f s mall
dimensions and interrupted activity opened
O n the 23 rd A pril (an other fu ll m oo n) the O bserva
tory instru ments became agitated the activity o f the
craters increased and o n th e evening o f the 24 th
plend id lavas descended the cone in various directions
s
attracti ng o n the same night the visits o f a great m any
str angers A ll these lava stream s were nearly exhausted
o n th e morning of the 2 5 th ; only one remained which
issued fro m the base o f the cone not far from the spot
whence that o f the preceding month had issued N um
bers of visitors attracted by the splendour Of the lava
streams o f the preceding night which they supposed
still co ntinued soon arrived but finding them exhauste d
were for the most par t conducted by their guides to see
the o ne still flowing It w a s al m ost inaccessible and
to reach it o ne had to walk over the rough inequalities
of the scori ae It took me two h ours to get there from
the O bservatory when I visited it that morning and
therefore I endeavoured to d issuade those who wished
to visit it at night from the attempt but set o u t myself
fro m the O bserv a tory at 7 p m le aving my only
assistant there The instruments were agitated A fter
midnight the O bservatory was closed and m y assistant
retired to rest Late and unlucky visitors passed nu
observed with an escort o f ine x perienced guides at half
past 3 o clock in the morni ng of the 2 6th they were in
the A tria del Cavallo when the Vesuvian cone bec ame
r ent in a north westerly direction the fissure c o m me nc
ing at the little cone which disappeare d and extending
to the A tri a del C a v allo wh e nce a CO io us torr e nt of
p
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T
F A AL A
CC I D E N TS
IT O R
V Is
To
s
87
.
lava issued T wo larg e craters formed at the summit
o f the mountain
discharging numerous incandescent
proj ectiles with white ashes and glittering with par
ticle so f mica which frequently recurred
A cloud o f smoke enveloped these unfortunates who
were under a hail o f burning proj ectiles and close to
the lava torrent S ome were buried beneath it* and
d isappeared for ever
two dead bodies were picked up
and eleven grievously inj ured o ne o f whom died close
to the O bservatory H e alone revealed his nam e
Antonio Giannone I learne d afterwards that he was
a fine young fello w and A ssistant P rofessor in o ne o f
the Universitie s
A ssistant P rofessors Signor Franco who is a priest
and S ignor Francesco Cozzolino a priest also entrusted
with the festive mass for the O bservatory hastened to
assist the dying O n my o w n return thither the sad
spectacle o f the d ead and dying awaited me ; the former
were conveyed through the assistance o f the municipal
Officer o f R esin a to the Cemetery and the latter to the
H ospital But we must leave thi s scene o f grief and
sorro w and return to the eruption
The fissure o f the cone on the north west side was
l arge and deep and e x tended into the A tria d el Cavallo
about 3 0 0 metres N o mouth opened along the cleft o f
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ght y ung medi ca l students p ish e d beneath th l
w ith
a ll y o uth s f go d p o mis
Th y w
e ;
o th e sunk n w n by na m e
thei n m sw ill b e reco d d o n the m ble m o num ent t b e e cte d
Gi o l mo P ans
ini A nt nio a nd
t o y T h ey
th O b s
nea
M auriz i F ggi co mo F n s Binetti d a M lf ttu Giusepp
i da T rani and Gio v anni B us
co S p zz af
co
Ca bo ne da Bari F rances
s
ima and V itangelo P o l i
d a Cas
amas
Ei
o
r
r
r
a
r
e rv a
e
ra
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e
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e
o
r
er
o
a
,
r
ere
o
a re :
ra
r
o
err
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,
e
e
r
o
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ce c o
e
r
o
a
av a ,
o
ar
e
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e
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e
T H E LA TE E RU P TI ON
88
V E SU V I U S
0 F
.
the cone itself ; all the lava issued from that part which
extended into the A tria From previous experience I
sho uld hav e expected to have see n the formation of
adventitio u s cones along the w idest part o f the fissure
which is never that most elevated and these discharging
fro m their su m m its mrifo rm matter frequently mixed
with pr o j ectiles and fro m their base lava ; b ut o n this
occasion no cone appeared at the w idest part of the
fissure but a long hillock w a s for m ed like a little chai n
of mountains one point o f w hich was elevated about
fifty m etres above the plain be neath and bearing no
resemblance to a cone
A nother fissure ope ned in the cone on the south side
w hich did not extend to the base and lava issued fro m
this and flowed in the direction O f the Cam aldoli
S tream s o f less importance furrowed the cone in other
directions but the largest quantity of lava proceeded
from the fissure in the A tria del Cavallo belo w the
hillock or miniature chain of collines j ust described
This lava stream was for some tim e restrained w ithin
the A tria del Cavallo among the holes and inequalities
but these bei ng filled up and
o f the lav a s of 1 8 7 1
overcome it divided into two branches— the smaller one
flowi ng through a hollo w which separated the lavas o f
1 8 6 7 from those Of 1 8 7 1 and made its w ay over the
lavas o f 1 8 5 8 threatening I te sina but stopped as soon as
it reached the first cultivated ground the larger branch
precipitate d itself into the Fossa della V e tra na occupy
ing the whole width about 8 0 0 metres
and traversing
the entire length of
metres in thre e hours It
dashed i nto the Fossa di Faraone here it again divided
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CO U R S E O F LA V A S T R E AM S
89
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into two streams o ne overlyi ng the lava o f 1 8 68 o n the
P lain Of the N ovelle partially covering the cultivated
ground and country houses ; the other flo w ing on
th rough the Fossa di F a rag lio ne over the lava o f 1 8 5 5
reached the v illages of Massa and S t S ebastiano
covering a portion o f the houses and thence continued
its course through the bed of a foss o r trench w hich
contrary to my advice had been excavated after the
eruption of 1 8 5 5 in the expectation of diverting the
cour se o f that lava I did not fail to O bserve that the
rains which previously descended through these s teep
channels would in future be kept back to filtrate
through the scori ae without ever reachi ng the new
channel
The lava o f this eruption meeting with this said ex
c a v a tio n flowed into it instead of pursui ng its road over
the lava o f 1 8 5 5 a nd thus invaded highly cultivated
groun d and towns o f considerable value extending to
the very wall s o f a country house belo nging to the cele
b ra te d painter
Luca Giordano
This lava stream
h aving surmounted the obstacles which th e heaps o f
scori ae in the A tria del Cavallo presented to it ran w i th
great velocity (notwithstanding its being greatly widened
so that between 1 0 a m
o u t in the Fossa del Vetrano )
a nd 1 1 p m it traversed about five kil ometres of road
occupyi ng a surface o f five to six square kilometres
If it had no t greatly slackened after midn ight fro m the
failure of supply at its source in t w enty four hours
more by occupying P onticelli it would have reached
N aples and flowed into the sea
Although I had Often visited the two villages o f
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90
LA T E E RU PTI ON
T HE
V ES U V I U S
0 F
.
Massa and S t S ebastiano previously greatly inj ured by
the lava o f 1 85 5 yet I could not well estimate upon
no w seeing them again the number of houses which
had disappeared Massa seemed to me diminished by
about one third and S t S ebastiano by somewhat less
than a fourth But the way of escape was open to the
inhabitants o f Massa ; whilst a great river o f lava
occ upying the road leading to S t G iorgio a Cremano
would have hindered the fligh t of the inhabitants o f
S t S ebastiano if they had bee n dilator y The lava
stream no w separating the two villages is little less
than a kilometre in width and is about s
ix metres in
height
O n th e night o f the 2 6th A pril the O bservato ry lay
bet ween two torrents o f fire which emitted an ins
uf
fer
able heat The glass in the w indow fra mes especially
o n the V e trana side was hot and cracking and a s mell
The cone
o f scorching was perceptible in the rooms
besides being furrowed by the lav a streams j ust described
was traversed by several others which appeared and dis
appeared I t seemed completely perforated and the
lava oozed as it were through its whole surface I
cannot better ex press this phenomenon than by s aying
I n the day time the cone
that V esuv iusswea ted fire
appeared momentarily covered with white s team j ets
(fumaroles) which looked like flakes o f cotton against
the dark mountain side appearing and disappearing a t
brief intervals
S i multaneously with the grand fissure o f the cone two
large craters opened at the summit discharging with a
dr e adful noise audible a t a great distance an i mmen s
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T E RROR A N D
F
L I G H T O F I N H AB IT AN T S
91
.
cloud o f smo ke and ashes with bombs and flakes rising
"
1
3
to the height of 0 0 metres above the brim of lava (sull
i)
s
The white ashe sbefore described although
o rlo d e es
they did not fall beyond the Cro c ella w ere carried by
the wind as far as Cosenza fro m whence they were sent
to me by D r Conti These ej ections were followed by
dark sand with lapill i and small fragments o f s e ori m o f
the same colour The smoke driven up with violence
assumed the usual aspect o f a pine tree o f so sad a
colour that it reminded us o f the shado w y elm of
Virgil s dreams u lmusOp a ca
Fro m the trunk
and branches of the pine tree cloud fell a rain of
incandescent material which frequently covered all the
cone The lapilli and the ashes were carried to greater
distances
The victims Of the morning o f the 2 6 th the torrents
of fire which threatened R esina Bosco and Torre
A nnunziata and which devastated the fertile country
o f the N ovelle
o f Massa S t S eb astiano and Cercola
the two partially buried villages the continual and
threatening growlings of the craters caused s u ch terror
that numbers fled from their dwellings near the m oun
tai n into N aples and several in N aples went to Rome o r
to other places Very many delayed from the knowledge
that I was in the O bservatory and held themselves in
readiness for flight whenever I should abandon it
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I f thi seno
sh eig ht O f proj ec tio n r ea lly m e ans, th a t a b o v e the
brim o f the c rat er, it inv o lv esa n initia l v elo city o f proj ectio n O f abo v e
British ) p er se co nd
60 0 fe e t (
O bs
er va tio nso f the h e ight o f a s
ce nt o f v o l c a nic bl o c k sare a l wa y s
diffic ult and d eceptive, and nev er free fro m erro r — T ra ns
la to r
rm o u
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.
.
92
T
LA T E E RUPTI ON
HE
0 F
V E S U V I US
.
rapidity with which the vast torrent of fire
assailed the houses
in these villages) and the great
heat w hich spread to a di stance scarcely allowed the
fugitives to carry a w ay any of their belo ngings ; m any
The authorities vied with
w ere co m pletely destitute
each other in zealous e fforts to relieve the distress and
the m u nicip ality of N aples sheltered and fe d the wretched
beings for many days
The igneous period o f the eruption was short for o n
the morni ng o f the 27 th the lava stream beari ng do w n
havi ng covered a few cultivated fields
u pon R esina
stopped ; the lava descending from the summit o f the
mountain towards the Camaldoli also stopped ; and the
great lava torrent which passed the sho ulders of the
O bservatory through th e Fossa della V e trana lowered
the level o f its surface belo w thos e o f its two sid es
which appeared like two parallel ramparts above it
If these streams h a d continued o n the 2 7th flo wing
in the sam e manner as th e y d id on the night o f the
they would have reached the sea bringing
2 6th
destruction to the ver y walls of N aples
But before leaving the subj ect o f these lavasI mus t
narrate an important fact to which I was witness and
which w a sthrice repeated near the banks o f the gr eat
A t three
river o f fire t hat ran close to the O bservatory
several points and at different times I observed great
balls o f black smoke issue from the lava d riven up with
continued violence as if fro m a crater ; through the
smoke I fre q uently obser ved numerous proj ectiles thrown
up into the air but I could no t say whether with noise
o r in silence
for the noise o f the central crater was
T he
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T H E LA T E E RU P TI O N
94
V ESU V IU
or
s
.
served in the Fossa d ella V e tra na w hich existed for
t w enty m inutes and then d i sappeare d and which were
not at all in a continuous line and could not be sup
posed to correspond with any fissure beneath constitute
a circumstance w hich if not ne w is evident for the first
time and cause the recognition Of a power in the lava
itself to for m eruptive fumaroles (2 )
T he i g neous period of the er u ption having terminated
o n the evening of the 2 7 th the a shes lapill i and pro
je c tile s becam e a little more abundant w hilst the
roaring noises o f the craters apparently became greater
The pine tree cloud w a s of a darker colour and was
furrowed by continual lightning visible by daylight
from the O bservatory Many writers on th e subj ec t of
Vesuvius affir m that the flashes which appear thro ug h
th e s moke cloud were l ightning unaccompanied w ith
thunder but they studied the phenomena from N aples
or some place more or less distant fro m the crater
where the report of the thunder was inau dible or could
not be distingui shed from the bellowing and detonation
of the mo u ntain The fact is that these flashes were
constantly followed by thunder after an interval Of
about seven seconds * When the flash was very short a
Simple noise like the report of a gun was heard but if
it were lo ng a protr a cted sound like that fro m torn
pape r ensued
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A ssuming th ese flashesto h v e emana t e d fro m so m ewh ere within
the l u dy o lu m e o f s
tea m a nd d ust ll e d the h ea d o f the pine
t e thisint l w o u ld indi te th t th e m ean h ight o f thisc l o u dy
V l um
it s
e lf w as no t m
th u snd fe et a b v the
e th a n a b o u t f u
t p o f th
c ne ;
nd
if s
o
tha t is no t e y fa f o m the lim it in
h eight o f p j tio n o f the d u st nd l apill i — T ra nslator
’
i
a
c o
r e,
o
o
v
”
e rv a
ca
e
a
or
e
“
ca
o
ro e c
a
,
e
o
r
v
,
a
o
r
a
r
o
r
;
e
F
AL L O F
P
RO J E C TI LE S
AN D
TE
MP E S T
95
.
O n the 28th the ashes and lapilli continuing to fall
abundantly darkened the air yet without diminishing
the terrible noise ; at R esina P ortici S t Giorgio a
Cremano N aples etc terror was universal
O n the 29 th w ith a strong wind blo w ing from the
east scori ae o f such a size fell at the O bservatory th at
the glass of the w indows unprotected by external blinds
w a sbro k en
The noise from the crater continued but
the p ro je c tile srose to a less height indicati ng a dimi
nu tio n in the dynamic power o f the eruption
To w ards
m idni g ht the noise of the craters was no lo nger con
tinu o u s and recurred w ith less force and for shor ter in
terv als A lmost at the same hour a tempest burst over
the Campania w ith loud thunder and a little rain The
grass the seeds the vine tendrils the leaves and tops of
the trees dried up immed iately and the country was
changed from spring to winter The storm altho ugh
repeated o n the follo w ing days passed away by degrees
and thus the floods which I strongly feared did not
occur Almost always after great eruptions of Vesuvius
stor m s o f heavy rain have followed and the ground
being covered with ashes the water could not filtra te
through into the soil but descended in m uddy t orrents
over the adj acent country occasioni ng as much damage
as the fire itself
O n the 3 0 th the detonations were very few and the
smoke issued only at intervals and by the l st May the
eruption w ascompletely over
When the smoke had cleared O ff the figure of the
cone was seen to be changed (V id e P late 5 A )
The gro u nd was perpetually disturbed whilst the
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T H E LA T E E R U PT I ON
96
0 F
V E SU V I U S
.
Volcano raged so that the O bservatory os cillated con
S o me shocks were felt not only in the adj a
tinu ally
cent territory but at a greater distance at Mo nto v i and
else w here The oscillations at the O bservatory were
ch iefly und u latory from N E to S W They w ere o b
served for some d ays after the termination of the e rup
tion but no t continuously altho u gh they maintained
some intensity
If we refer to J anuary 1 8 7 1 we shall find that that
eruption w a s preceded by several earthquakes among
w hich were those o f the m onths o f O ctober N ovember
and D ecember in the previous year that wrought s u ch
destruction in Calabria a nd e sp e cially in the province
o f Cosenza
if w e consider that as only the last phase
we shall find that it was preceded by great Shocks o f
earthquake that devastated some regions of Greece (3 )
The great q u antity o f lapilli which fell buried the
s
co riee with which the Vesuvius cone was covere d so
that it became somewh a t m ore difficult to ascend to the
sum m it a nd much less d iffic u lt to descend H aving
reached the top O f the m ou ntain I found a large crater
di v ided into two parts by w hat seemed a cyclopean
wall
The two abysses had vertical Sides and revealed
the internal structure o f the cone
Their vertical
depth was 2 5 0 metres ; and beyond that I observed a
sort of t unnel perforated in the rock with a coveri ng
a rch raised above the botto m of th e eastern abyss about
1 2 metres j u d ging by the eye
The interior walls o f
the crater showe d neither the usual stalactitic sco rim
nor s u bli m ations nor fumaroles but alternate beds o f
scori ae and of compact lava The fumaroles and sub li
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T H E LA T E E RUP TI O N
98
0 F
V E SU V I U S
.
eruption occupies a surface o f about five square kilo
metres ; allowing an average thickness o f four metres
we o btain a m ass o f twenty millions of cubic m etres
A bout three fifths of this lava did no inj ury being de
posited upon other pre existing lava
H owever the
lava in the N o v elle which was deposited upon the lava of
1 8 5 8 covered quarries o f the best stone which had been
worked at the ti m e covered many paths that had been
cleared and b u ried the ne w Church O f S t Michele
with some houses that surrounded it which had been
rebuilt o n the site of the former church which was
covered by the lava o f 1 8 68 The destruction of land
in occupation of buildings and o f crops e x ceeded th ree
million francs in value Many proposals for relieving
the sufferers have been received Wishing to aid in
this benevolent work I gave a public lecture admission
for each pe rson being one franc and this lecture from
notes badly taken was printed by private Speculation
and I was compelled to rep udiate the report Of it
throu gh the public papers
The evolution s of carbonic acid (mofette) which usually
appear at the end o f great Ves uvian eruptions at low
situ a ted spots o r hollows with very rare e x ceptions
were observed o n this occasion a few days after the
eruption had completely ceased They appeared in the
direction of R esina I found the most elevated at Tironi
and the m ost n u merous betwee n La Favorita and the
Bosco B e ale di P ortici
The water in wells was o n this occasion neither d efi
cient nor scarce prev ious to the eruption but was very
acid after the appearance of the carbonic acid evolutions
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REMA RK S O N
P
H E N O ME N A
99
.
in those neighbourhoods in w h ich they abound ed
H aving stated that the disastrou s co nfla g ra tio n o f the
2 6th A pril ough t in m y opinion to be regarded as
the last phase o f a long period of eruption which
commenced at the beginning of 1 8 7 1 I consider it
right to discuss the question at some what greater
length
N ot only from twenty years personal observations but
fro m the attentive study o faccounts O f previous eruptions
I have found that when the central crater a w akens with
sm all eruptions after a cert ain time of previous repose
these almost al w ays have a long duration and after
v arious phases o f increase and decrease terminate in a
great eccentric eruption that is to say with the p ro
duction of an aperture from which a copious lava
stream issues
T he eruptions o f 1 8 5 8 1 8 61 1 868 and
1 8 72 furnish the most recent examples of what I af
firm
I m ight cite many others o f earlier date but I shall
content myself with recording the greatest c o nfla g ra tio n
of this century that of O ctober 1 8 22
Before the erection of the Vesuvian O bservatory it
was i m possible to Obtain a consecuti v e account of all
the phases which the Volcano presented but we gene
rally Obtained the description of the more splendid
phases o f the eruption which arrested the attention
of everyone H ence notices o f the small phenomena
w hich preceded a great eruption are frequently wanting
We cannot always ascertain whether the fu m aroles o f
the craters became active and at what periods what was
their temperature and w hat the diverse nature of their
emanations etc whether and w hen any ch ange in the
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T H E LA T E
100
E
RU PTI O N
VES U V I U S
O F
.
crater with slight erupti ve manifestations O ccurred ; dis
charges which so m eti m es commenced in the bottom o f a
crater beco m ing active and so are inv isible at N aples
ked whether the inverse proposition
B u t it m a y b e a s
be equally true that is w hether all the g reat eruptions
of our Volcano w ere preceded by small fiery manifesta
tions o f lo ng duration 1 There have undoubtedly been
great er u ptions not preceded by s m all central eruptions
but these a lso had their period of preparation or p re c u r
sory signs After the great eruption of 1 8 5 0 Vesuvi u s
remained in apparent repose until the end of May 1 8 5 5
w hen there was an eccentric er u ption and a great flo w
of lava lasting t w enty seven days
But for a year
before the fumaroles on the top o f the mountai n had
d
a cquired great activity their temperat u re increased a n
hydrochloric and sulphuric acid bec a me m ore ab u ndant
and generated the usual coloured products o n th e adj a
cent sc o riee Finally in the month of J anuary a crater
w a sfor m ed by falling in of the ground and although it
did no t discharge fire yet it poured forth dense smoke
This was the beginning of the fissure manifested four
months afterwards
Ignazio S orrentino who spent a long life in the study
o f Vesuvius and frequently ascended it considered the
increa se of those yello w products— which are chiefly
chlorides of iron but w ere at that time mistaken for
s
ulphur— as the Sign o f an approaching eruption
The only grave Obj ection that c a n be alleged is that
o f the memorable er u ption of 1 6 3 1 which surprised the
neighbouring population so suddenly that many perished
miserably surrounded or covered with lava But that
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T H E LA T E E RUP TI O N O F V E SU V I U S
102
.
watched they would have undoubte dly indicated the
gre a t increase in the activity Of the Volcano The
pert urbations o n the 2 3 rd were steadily increasing
and on the evening of the 2 5 th they were much
stronger than o n the 2 4 th but o n the morning o f
the 2 6th they ha d become extraordinarily strong ; they
must therefore have increased considerably during the
n ight
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II
N AT U R E
OF
.
T HE
LAV AS
.
W H E N the Observer is near the source o f the lava he
sees m atter in a state of fusion w hich like a torre nt o f
liquid fire runs along with more o r less i m petuosity
between two banks formed by itself But as soon as the
surface o f the torrent cools to the point of congelatio n
it loses the Sple ndour of its first incandescence The
part which begins to harden breaks readily in some
lavas into frag m ents which float on the viscous fluid
bene a th ; these increasing in number with distance fro m
the source conceal the molten matter beneath and
retard its progress and at last nothing is seen but the
m ore o r less red hot s
These lava s
c o rim moving along
I shall call L a v a swith frag menta ry sc o rice
O n other occasions a skin forms on the surface of the
l ava which g ra dually thickening keeps flexible for
som e time and then w rinkles or swells o r extends and
breaks to give egress to the hot fluid within w hich in
its turn skins over and repeats the same phenomena
”
This I shall call L a v a swith a united surfa ce
T hese in their course discharge less smoke than the
first draw out more easily into threads and when cold
h ave a d ark colo u r so m ething like bitumen o r pitch
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T H E LA T E E RUP TI ON O F V E SU V I U S
104
.
c o riw,
n
m
e
t
a ry s
g
retched
when
st
f
breaks easily discharges smoke copiously , and when
hardened has a more bluish tint like clods of upturned
earth (fo rma to (li z o lle) It is noisy in its course
because the incoherent scori ae that it carries along strike
and crunch against each other ; the other lava flows
silently except for a sort of crackling arising from the
a ctu al fracturing up of the solid skin by distension from
the liquid matter within
If required to give the
mineralo g ical characteristics of this lava I would say
th a t it w a s rich in leucite and contained little or
no pyroxene the fragmentary lava o n the contrary is
poor in leucite and rich in pyroxene The lavas of
united surface character ; those O f
1 8 7 1 were of the
1 8 7 2 w ere
fragmentary with some characteristics
w hich I shall d escribe :
1 They were of the clearest tint I have ever seen
w hen regarded superficially but when broken
th e fracture was darker than any other lava
2 They had very little leucite and abounded in
pyroxene and olivine and sometimes contained a
few crystals of amphibole
3 Their specific gravity varied with their porosity ;
the m ost co m pact attained
These lavas carried along in their course a
4
quantity of scori es which had long been sub
je c te d to the actio n O f the acids of the fumaroles
close to the craters and also a great many
bo m bs (bo mbe) — that is round masses similar to
those ej ected from craters
These varied in
w ith
T he la va
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T H E LA T E E RUP TI O N
106
a
very
i g
VESU VIU S
.
m agnetoscope
w as
c ep t n
OF
invariably magneto polar not
pie c e s of the bombs w h ether
the cra te r or c a rried alo ng w ith the
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III
F U MAR O LE S
.
T HE
OF
LAV AS
.
generally issue s from all lava whe n it cools
d own to a certain degree hence it is more abundant at
the e d ges o f the fiery torrent o r is liberated from the
scori ae that form o n its surface But w hen the lava
stops the smoke issues only from certain vent holes
thro ugh w hich we can still see th e fire and at the edge
of which di fferent amorpho u s or crystallized matters
collect by sublimation These centres of heat o f more
or less duration are the fumaroles of the lavas I
believe I have o n other occasion sshown that a fu marole
is nothing but a com m unication between the m ore or
less cooled and hardened surface of the lava and the
interior which is still incandescent S ome fumaroles
last b u t a d a y others preserve their activity for weeks
m onths o r years according to the depth o f lava through
which they penetrate ; and w hen they cease to be active
th at is when the sublimations are formed or smoke or
other wrifo rm matters issue fro m them they still retain
a rather elevated temperat ure In the lavas O f 1 85 8
in a place where they had a transverse w idth of 1 5 0
m etres a vent hole may still be found where the ther
m o m e te r registers 60 and the scori ae are warm
S ome
S MO KE
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T H E LA T E E RUP TI ON
108
V E SU vIU
0 F
s
.
times while the lava is in proces s o f cooling ne w
fumaroles appear in which the fire is visible This
phenomenon which appeared m arvellous and ine x pli
cable w hen I first Observed it in 1 85 5 is now very
e a sily understood ; the cooled a nd hardened crust Of the
lava fractures with noise and suddenly and so a ne w
c o m munication is opened with the incandescent lava
below thus creating a new fumarole
A s the smoke o f the fluid lava is perfectly neutral
that is neither acid no r alkaline so the fumaroles at the
first period of t heir existence with sublimations o f sea
salt mi x ed frequently with oxide o f copper either in
black powder or in Shining lamin ae ought also to be
neutral But if the fumarole continues active hydro
chloric acid issues with the smoke and Ofte n some time
after sulphuric acid Then the sublimations turn first
yello w then green and more rarely azure The ch e
mical reactions Show that these sublimations are chlo
rides o r sulpho chlorides and sometimes sulphides and
they afford reactions indicative o f soda magnesia
copper lead and traces o f other substances not e xclu d
ing am m onia w hich I m u st Speak o f separately
This
I have Observed is the general law with the fumaroles
o f the tranquil lavas which occ u r with long and mode
rate eruptions— for instance the lavas o f 1 87 1 and even
those of 1 8 72 preceding the 2 6th A pril
But in the great lavas o f the great c o nflag ratio nsof
Vesuvius chloride of iron more or less in com b inatio n
with all the other substances above mentioned changes
the appearance o f the sublimations The fumaroles in
the lava o f the 2 6th A pril freque ntly indicated chloride
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T H E LA T E E RUP TI ON O F V E SU V I U S
110
.
fo u nd a fumarole w ith a small quantity Of micaceo us
pero x ide o f iro n e v idently in a state o f formation ; but
th is w a sthe very spot where the lava became eruptive
and whence issued the column o f smoke which was so
w ell photographed— the place under the hill of A picella
4
A )
S
ee
P
late
(
I have enumerated the products which are constantly
collected in fu maroles although they are not all found
at the same time o r place in order to Show that the
s u blimations follow a certain law in their appeara nce
T eno rite for instance was for m erly considered an acci
dental product o f certain eruptions and I have always
fo u nd it ; but if yo u visit the fumarole when the acids
have had time to transform it yo u will no longer see it
”
I found the crystallized chloride o f lead or cotunnite
as it is called for the first time in the lavas o f 1 85 5
and thought it a singular circumstance ; but from that
time I recognised it in all the lavas though not always
so beautiful and abundant ; and even when not found
as a distinct substance I observed it in combination with
chloride o f copper I n the lavas o f the 2 6th A pril
9“
c o tunnite and teno rite
were no t very abundant because
the chloride o f iron disturbed the greater number O f the
sublimations I found sal ammoniac very abundantly
o n the fumaroles of the lavas that invaded the cultivated
ro
u nd
A
lthough
chloride
o f ammonia
contrary
to
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hl d
t
t yt
p
d
t l
t h
y t
h d
l
l d
ht l t
y
thd
pp
th h
k t l g y
b t
yt
CO T U N U I T E , c o ri e o f ea , in w i e , u sr o u s
a cic ular c r sals
,
,
o f th e
rim e ric s se m , eas
il s
c ra c e , S
p gr , 5 2 3 8
T E N O R IT E ,
e ro x i e o f c o
e r, in
in, e x ag o na
a es o r s
c al es
,
ra n su ce n w e n v e r
hin, d a r
ra , o f t he cu ic s sem
se e
;
—T r a ns
ar
a nd u s
tro u s S p g r a o u
la tor
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l pl t
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b
yt
CH E M I C AL P RO D U C T S I N
F U
M AR
O I .E S
111
.
opinion w a s not wanting in the sublimations Of the
fum aroles o f the lavas deposited o n other lavas yet it
w a sneither abun d ant nor crystallized but combined in
small quantities with other substances It appeared in
great abundance in all the fumaroles of lavas which
covered cultivated or woody ground A t first it was
scarce enough and mixed w ith chloride o f sodium ; but
w hen the rains came the sea salt was washed a w ay and
sal ammoniac formed beautiful crystals nearly free from
adventitious matters as was the case with the fu ma roles
of the last lava A fter wards when chloride of iron
was produced ferro chloride of ammonia was found
Crystals of sal ammoniac were sometimes found of a
beautiful amber yello w This colour was in the Opinio n
of my colleague P rofessor S cacchi produced by such
small traces Of chloride o f iron that neither P rofessor
G u is
c ardi nor I nor indeed any other chemists to whom
I s u bmitted specimens for examination could detect
any W hat I can affirm with certainty is that these
limpid crystals of a yellow colour were almos t al w ays
attached to an amorphous substance soluble in w ater
composed Of various chlorides in which iron w a s often
detected
From these remarks it is evident that in the tranquil
lavas the sublimations appear with a certain order of
succession and in the violent lavas and those which
flo w most copiously they are m ore complicated and
render both chemical analysis and spectroscopic
researchesmore di fficult N otwithstanding I observed
traces of lithium and thallium which I h a d previously
perceived in some sublim ations of 1 8 7 1 I purpose
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T H E LA T E E RU P TI O N O F V E SU V I U S
1 12
.
submitting many sublimations w hich I have collected
to more co m plete spectroscopic inve stigation although I
that the discovery of traces o f certain
u aded
a m pers
bodies in the sublimatio ns or in the lavas is a matter o f
I must
m all importance to the science of volcanoes
s
o
ever
that
calcium
w
a s discovered o n this occa
h
w
s
a
y
ion in great abundance not only by the spectroscope
s
but also by chemical analysis S ulphate of lime has
Often been found in l a rger or sm aller proportions but
thi sw a sthe fir st time I ha d observed chloride of calcium
both close to the craters and also in the sublim a tions of
the fu maroles upon the lavas The white stalactites
w hich I c o llected beneath the great mass or bo m b
ab o ve described were almost exclusively composed of
chloride o f calcium and o nly a few g reen d rops
manifested w ith the usual re agents the p re se nc e of
iron
I did not fail to look ofte n at the sp ectrum of the
flowing lav s covered with the smoke which issued from
them but I always had a continuous spectr um The
pectroscope employed was Ho flma nn s construction
s
w ith direct vision ; but I think it would be better on
other occasions to use a spectroscope combined with a
telescope like th ose used by astronomers
But avoidi ng minute particulars o f these sublimates
let us see what is the general direction and the order of
their appearance
S ublimations are generally o xid es
chlorides and sulphates sometimes sulphides A mong
the oxides we m u st enumerate in the first place tenor
e
ero lig is
te or micaceous peroxide of iron
and
The
f
y
first is al most al ways found at the commencement o f
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T H E LA T E E RUP TI ON O F V E SU V I U S
1 14
h ighest
.
When these subli mations are greenish they
beco m e far less sol uble than a t first The yello w so
co m m o n at a certain period on the fumaroles of the
tr a nq uil l ava s ne v er attracted attention before I first
exa m ined it doubtless because it was considered
chloride O f iron and yet in small eruptions this is onl y
found close to the dischargi ng m ouths and never in the
ubli m ations of the fumaroles o f th e l a va ; but on the
s
other hand it isthe mo st copious a nd com m on product
This probably also
o n the lavas of the great eruptions
accounts for th e fact that lead which is so Obvious in
the fu maroles of the lavas had never pre v io u sly been
ob served I n 1 8 5 5 I noticed the crystallized chloride
of lead in a fumarole in the Fossa della V e trana and
this ind u ced m e al w ays to look for it o n the fumaroles
o f the later lavas ; and I ascertained that
if it did not
always appear as a distinct m ineral it was easi ly
disco v ered in combination with other chlorides The
speci m ens which I have collected are no t the most
beautiful but the presence of lead in the sublimations
is not less co m m on
Micaceous peroxide of iro n when found on the lava
has been m ostly conveyed fro m the eruptive mouths as I
have already stated and perhaps n ever so abundantly
and evidently as on this occasion The lava of the 2 6th
of A pril carried along a l arge qu antity o f round m asses
o r bo m bs
among which were found
v arying in s ize
antecedent lava more O r less covered with micaceous
iro n either collected in the cavities of the lav a or in
c o rp o ra te d with its mass
S ometi m e s the micaceous
iron appears like litt le veins in the paste of ne w lava
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CO N S T R U CTI O N O F
T HE
B
O MB S
1 15
.
enveloping the e x terior of these rounded masses an
exterior compact and li thoi d al and not resembling
scori ae A mong these spherical m asses I found o ne o f
enormous size four to five m etres in diam eter which
having broken up where the exterior envelope was
thinnest I found filled w ith a great mass of lapilli and
fragme nts o f other lavas co v ered w ith micaceous iron
This bomb stil l p reserves (J une 5 th) a n elevated tem
p era ture within and emits smoke a nd hydrochloric acid
which meeting the micaceous iron discovered by break
ing the envelope with blows of a hammer transfor m s
i t superficially into chloride of iron sho w ing most
clearly how o n some occasions at least chloride of iron
isformed from the o x ide w hich precedes it That those
lapilli and the pieces of lava wer e solid when enveloped
in the paste of the ne w lava w e infer from seeing the
impressions o n the inside o f the said envelope The
chloride of calcium which I fo und in this Spherical
m ass almost pure caused me to suspect that the sul
phate of lime which is so Ofte n fo und on Vesuvius is a
transformation o f the chloride produced by the c ontact
o f sulphurous acid which easily becomes transformed
into sulphuric acid
The hydrochloric acid which
escapes from a fumarole co m ing into contact with the
scori ae near its mouth prod u ces chloride of iro n which
is therefore no t always obtained by sublimation al
though when the temperat u re isvery high chloride o f
iron is conveyed from the interior of the lava and sub
li m es o n the exterior and colder parts ; for instance the
C hloride o f iron which issues fro m the eruptive cones is
sometimes found sublimed on the rocks o f Monte di
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1 16
T H E LA T E E RUP TI ON
0
F
V E SU V I US
.
S om m a When chl o ride of iron has been produced by
s
u bli m ation we m ay collect it inside a glass bell placed
over the fumarole or u pon a piece of brick ; but w hen
it is p rod u ced by the action of hydrochloric acid on the
c o riee themselve s
s
c o riaa it w ill only be fo u nd o n th e s
If therefore the origin of m ic a ceous peroxide o f iron
w ere d u e to the d ecomposition of th e sesq u i chl o ride o f
iron requiring a m ore elevated temperature fo r its d e c o m
position it wo u ld follo w that its genesis w ould be easier
n ear the d ischargi ng m ouths a nd m ore di f
ficult on the
lavas but there the fa ct was verified : fo r exam ple in
the great bo m b on the fu marole w here w e obser v ed m i
\V e
c a c e o u s iron tran sformed into chloride of iron
may therefore consider it p ro v ed that some chlorides — for
ins tance chloride of sodiu m — iss u e from the lava it self
either being there p ie exi stent o r being for m ed there ;
and that others are deri v ed from the o x ides w hich pre
cede the m as undoubtedly is the case w ith chloride of
copper ; hence the theory t hat deri v es the oxides
al w ays fro m the chlorides cannot be considered tr ue
G ranti ng that this theory m ight be a pplicable to the
origin of micaceous iron we Should still want to kno w
h o w it is fo u nd with the paste of the ne w lava itself
which forms the exterior coati ng of the bombs above
described
Many of the se roun d ed m asses w hich have been
rolled along by the lava contain scor iae partly d e c o m
po sed by th e long action O f the acid s found on the
fu maroles of the craters They disintegrate easily and
have a more or less yello w ish ti nt
In the greater
nu m ber of cases the interior o f these masses is formed
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T HE
L AT E
E
RU PTI O N
VE S U VI U S
0F
.
I have al w a ys obta in e d n e g a ti ve results
tha t the a tm osph e r e on the lavas contain e d an excess
o f c a rbonic a cid but a s these l a v a s had burnt m any
tr e es a nd it w a s
th a t carbonic a cid springs
h a d for m ed under the lava I nev e r considered it safe to
for m any conclusion on the subj e ct
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IV
BO MBS , LAP ILLI AN D A S HE S
.
bo mbs ej ec ted fro m the craters are like those
carried do w n by the lavas but of s maller si z e and they
seldo m er contain a nucleus si m ilar to those found in th e
latter W ith the bo mbs prop e rly so called m any pi e c e s
o f incandescent lava w ere thro w n up and in their fall
w ent beyond the base o f the cone
A quantity o f
s mall scori ae varying in siz e acco m panied thes e pro
c tile s a nd those frag ments w hich w e call lap illi fe ll
e
j
at a greater distance W ith the l a pilli and so me ti me s
w ithout the m th e s moke carried a very minute dust o r
sand w hich is gener ally c a ll e d ashes These ashes w h e n
W ash e d w ith w ater lose solubl e constituents which th e y
hav e coll e cted in the sm ok e such as chloride of sodiu m
and other chlorides and ofte n fre e acids The insol uble
part origin a tes in the detritus o f l a va and with the m icro
scop e w e can detec t abundant frag ments of those crys tals
which m ost frequently occur in the lava of the sam e
eruption
The l a vas o f 1 87 1 which w er e e minently leucitic and
rese mbl e d th e
al m ost entirely deprived o f pyroxene
ash e s w hich appeared to b e frag m ents o f crystals of
leucit e m ore o r less e nvelop e d in the paste o f th e lav a
so that having triturated th e scori ae of the l av a a nd
looked a t the po wder through the microscope it w a s
apparently quite the sam e as the ashes
T HE
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1 20
LA T E
T HE
E
RU PTI O N O F
s
vvw
v ns
b e ginning of th e e ruption of the 2 6th
A pril a w hit e s a nd fe ll in the A tria del Cav a llo close
co rize of 1 8 7 1
to the Cro c ella
w hich o n th e dark s
look e d like sno w Its fall had a li mi t so w e ll defin e d
th a t o ne p a ss e d w ithout a ny gr a d a tion fro m w hit e to
bl a ck H aving collect e d so m e o f this s a nd that v e ry
m orning I put it up in w hit e p a per for at th a t m o m ent
it w a si m possibl e for m e to exa mine it T a king it o u t
so m e days a fter I found it h ad beco m e r e ddish a nd
h a ving put it u nd e r th e m icroscop e I obs e rv e d th a t it w a s
exclusiv e ly for me d of littl e p e bbles m or e o r less round
of a tr ansp a r e nt Vitreous m a tter partly covered w ith a
re d subst a nc e
Fr a g m ents o f green crystals occurred
in this sand u pon which no re d w a s p e rc e ptibl e I
consult e d our e minen t cryst allogr a ph e r A rcang e lo
S cacchi w h e ther thes e little p e bbl e s w e r e l e ucit e a s I
suspe cted and w h e th e r the green particles w ere py
r o xe ne : he confir m e d m
y suspicion and re m arked that
the re d colour w a ssup e rfici a l only W e th e n w ash e d a
littl e of the s a nd in hot w a te r a nd sa w the p e bbl e s
beco m e w hitish ; but havi ng heated so m e on platinu m
w e observed th a t th e y first turne d black and th e n b e
c a m e p e rfe ctly w hite proving that the red w a sa d e posit
o f org a nic m a t t e r
To se e th e se leucites rounde d like
s m all p e bbl e s tr a nsporte d by a torrent d e prived of the
solubl e chlorides w hic h generally a cco mp a ny Vesuvian
a sh e s is a m a tter w orthy of a tt e ntion
W hilst heating
this s a n d u pon platinu m decrepit a tion wa s a udible
w hich indic a ted th e cracking o f so m e of th e littl e
pebbl e s It is e vident th e refor e th a t crysta ls o f l e ucite
rai sed to a certa in te m p e r a t ure m a y br eak a nd thus
w e can und e rstand h o w al most all Vesuvi a n ash e s con
B ut
at
th e
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V
T HE CR AT E R S AN D T HE I R F U MA R O LE S
.
greater part o f the l a va issu e d fro m the base o f the
gre a t fissure in the con e w hi c h I have d e scribed ; and
a lthough two other lava str e a m s d e scended fro m the top
o f the m ountain neither proce e d e d fro m the crater but
fro m a pertures near it T he gr e a t crater divided in two
as already described O p e n e d w id e on the m orning of the
2 6th A pril destro ying the bri m of the antecedent cr a t e r
a nd re m a ki ng it in an oth e r sh a p e w ith ej ected m att e r
exc e pt o n the south w e st side w here the bri m wassplit
(S e e P l a te
F ro m this doubl e crater copious s m oke bo m bs a nd
incandes cent scori ae w ith ashes a nd lapilli issued with
v iolence
and fro m the d e pths belo w cam e dre a dful
deton ations and b ello w ing s producing great te rror
A n d yet the lava poured o u t into the A tria del Cav allo
w ithout any noise and not eve n a colu mn o f s m oke
m a rked its origin o f iss ue — n a m ely fro m the fissure
W hen the eruption w a sov e r the sight o f the vertic al
w alls o f these d e e p cra t e rs of al most horizonta l
strata of scori ae and lithoid a l m asses with a fracture
fresh and as if they had never undergone the action of
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E
M A N A TI O N S A F T E R
T HE
U P TI O N
E R
1 23
.
or o f acid vapour s without recent scori ae and w ithout
fu ma roles w a s to m e a m arvellous spectacl e The
fu m aroles w e re al m ost all o n the bri ms of th e craters
w ith e m a n a tions o f hydrochloric and sulphurous aci d
In a fe w that w e r e m ore re m ov e d fro m th e bri m sul
In th e subli m a
p h u re tte d hydrog e n w a s p e rceptibl e
tions chloride of iron w a smost a bund a nt in co mbin a
tion w ith other chlorides for e xa m pl e o f sodiu m
This last chlorid e w a s fre
m agnesiu m and calciu m
qu e nt e ven am ong th e subli mations of the fum a rol e s of
th e l a vas and i t w a sthe first ti m e it w a se v er re marked
but I d o not think it w as the first ti m e th a t it w a s
e v e r produced : being in co m binatio n w ith chloride o f
iron and very d e liquesc e n t it d id not a ttr a ct attention
fro m anyon e In a hollo w fr a g m ent o f scori ae I o b
serv e d a yello wish substanc e which look e d lik e sulphur
in a viscid state and w hich boil e d a t a t e mp e ratur e of
and evolved hydrochloric a cid H aving coll e cted
this s ubstanc e and pour e d it into a glass phial it quickl y
coag ulated into an a m or phous m a ss of the s a m e colour ;
but b e for e I r e ach e d the O bserva tory I found th a t it
It consisted of a
ha d beco m e liquid by deliquescenc e
m ixture of th e aforesaid chlorid e s a ccording to an a na
lysis m ade by P rofe ssor S ilve stro Z inno a nd m yself In
so me fu m aroles w here I p e rceived the s me ll of sul
m
hydrogen
I
found
subli
ed
sul
hur
under
h
u
re
t
e
d
t
p
p
th e scori ae
A t the source o f the l a va str e a m that fl o w ed to w ards
the Cam aldoli o n the sea wa rd fl ank of Vesuvius I
observ e d large fum a roles o f stea m o nl y pure aqueous
v apour
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1 24
T HE
L AT E
E
RU PTI O N O F V E S U VI U S
.
no trac e
c a rbonic a cid
th e se
rol e s
th a t fa ct
th e re w a sno ne
l a te r p e riod
sinc e the first investig a tions of
D e vill e it is kno w n th a t carbonic a cid is found u nd e r
c e rta in conditions o n
v e ry su m mit of Ve 's
uvius
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1 26
T
HE
L
AT E
E
RU PTI O N
V E S U VI U S
or
.
h a ving a little pl a t e o r cylindrical c a vity o f
w ith tw o a r m s
gild e d bra ss a t the top (Figs 2 a nd
In th e pl a te a disc of alu miniu m m is sus
d d (1 d
p e nd e d by m e a ns of tw o silk fibr e s a nd to th e disc a
bent a little
v e ry fine a lu m iniu m w ir e is
T he disc h a s
a t the e nds a s a re th e ar m s (I d (l d
pl a te
a bout thr e e m illi m e tr e s lcss di a m e t e r than th e
T h e d i a m e t e r of th e pl a t e m a y v a ry w ithin cert ain
li m its but I h a v e found it conveni e nt to m a ke it
e ight e e n m illi m e tr e s
T he gl a ss tube a a (Fig
should
desc e nd b elo w th e b a se a sm uch a sit ris e s above it th a t
is thre e to four centi me tres The length o f the ind e x
is about o ne de ci m etre
T he upper ends of the tw o silk fibr e s by w hich the
disk and index a re suspend e d a re a ttach e d to th e top of
the glass tub e 0 by a contriv ance w hich p e r mits a
change in th e d ista nc e b e t w een the tw o points of sus
p e nsion and a scre w 10 is provi d ed to r a ise a nd lo w er
the disc w ith the index A t 72 a t the lo w e r part of the
tub e 0 ther e is a kind of torsion micro m et e r a rr ang e d
so as to bring the ind e x to the zero o f the scale e ngra v e d
o n the graduated ring B
w hich is for med of a strip of
T he
good paper pasted o n the rim of a gl a ss disc
ind e x m ust b e pl a ced a t the z e ro of th e scale a nd must
be so me di stanc e fro m the ends of th e arm s of the pl a te
T he pl a t e is about three
w ith w hich it is p a r a ll e l
m illi m etr e s d e ep
H aving levell e d the instru m ent so as to rend e r the
disc concentric w ith the pla t e a nd pla c e d the ind e x a t
z e ro it is obvious th a t if an e l e ctric cha rg e through the
w ir e It r e a ch th e plat e with the ar ms it w ill e lectrify
m a stic
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T HE
B
I F I LA R
E LE
CT R O ME T E R
1 27
.
the disc and index : the disc will have the O pposite
e l e ctricity
and the extre miti e s o f the index w ill take
the sa m e electricity as the a r m s and consequ e ntly the
ind e x w ill descri b e a n are m ore o r less gre a t T he
m otion of the i ndex is suffici e ntly slo w to allo w the eye
conv e n iently to follo w it H aving traverse d the first
a re
w hich I cal l the imp uls
iv e O ne the index returns
a nd
after only two oscillations co mes to rest a t what I
sh all c all the d efinite arc
\Vh e n the electric ch a rg e s a re o f very bri e f dur a tion
th e i m pulsive arcs are w ithin certain li mits propor tional
to the te nsmns and the r a tio bet w een the i mp ulsive and
d e finite arcs is expresse d by the follo wing equation
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66
(l3
)
a
B
tang
1
.
g
a
In which (3 is the i mp ulsi v e a rc and a the definit e are
sho wing that a co mes o u t ne a rly equal to 6 I n dry
w e a ther all goes perfectly w ithin the li mits of propor
tion and I can tell w heth e r during the ti me in w hic h
the ind e x traversed the i m pulsive a rc there w e r e a ny
d is
p ersio nsand o f w hat n a ture fo r if the definit e arc is
no t clos e to the li mit o f th e i m pulsive are it is a sign of
d is
io nshaving taken pl a ce during the m otions of the
p ers
index Every degree less in the definite arc denotes two
d e grees o f loss for the i m pulsive arc ; but as the ind e x
e mploys do uble the ti me trav e rsing the definite as it
do e s th e i mpulsive are w e m a y consider the loss of o ne
equa l to the loss of the oth e r
In e xc e ssi v ely damp w e a ther the index gives no d e fi
nite arc a nd it is necess a ry to r e sort to artifici al h e at in
order to dry the insulators The most si mple means I
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1 28
L AT E
T HE
ER
U PTI O N
V E S U VI U S
or
.
kno w o f is to hold th e instru me nt ov e r so m e hollo w
v e ss el w hich for th e ti m e is converte d into a stov e by
th e introduction o f a spirit l a mp
Fro m G a uss s for m ul a for th e b ifilar syste m o f instru
m e nts o f thi scl a ss w e l e a rn th a t th e m axi m u m s e nsitive
n e ss of such i nstru m e nts is gi v e n w h e n the l e ngth o f
th e susp e ndi ng fibr e s is gr e a test a nd th e d ist a nc e b e
t w e e n the m is s m allest w ith the w e ight of the m ov able
or rot a ti ng m e m b e r a mini m u m 5 and th e se e le me nts
b e ing th e s a me the sensitiven e ss of the instru ments is
invari a bl e
To so m e e lectro m eters in ord e r to a void errors of
par all a x a sm all t e l e scope w ith a m icro me te r wir e ha s
b e e n a dded ; but w ith a l ittle practice w e can re a d
In or d e r to obt ain
a ccurat e ly w ithout this r e fine m ent
co m p a r a tive m ea sur e me nts it is n e cess a ry to s e l e ct so me
given unit o f t e nsion I h ave obs e rved that by m aki ng
a nd
a g a lv a nic pil e of copp e r zin c a n d distill e d w ater
insulati ng it w e ll each pol e h a s a t e nsion w hich re
m ai ns the s a m e for m a ny days if th e conditions of
te mperature and th e m oistur e o f the surrounding at mo
ph e r e a re not very di ffe r e nt W ith thirty p airs of this
s
pil e e a ch e l e m ent h a ving t w e nty fiv e squa re centi metr e s
a ce I have on the e l e ctro m e t e r a d e finit e arc of
o f sur f
w ith the t e mperature o f th e a t m ospher e a t 2 0 C
fe r e nc e o f 4 to 5 C bet w e e n the ther
a nd w ith the di f
m o m e terso f th e psych ro m e t e r of A ug u st s constr u ction
T he first observ a tion w a sm ade t w enty four hours a fter
mounti ng the pil e For u nit of tension I took th a t w hich
corr e spond e d to a si ngl e p ai r th a t is the thirtieth p a rt
O th e r e lectro m ete rs m a y b e c o m
o f th e tot a l te nsion
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13 0
T HE
L AT E
E
RU PTI O N
0F
s
v r uv w
s
.
raise and
is
he
pen
cord
ich
is
sed
to
u
m
h
a
w
fff
lo w er the conductor
i is a copp e r w ire cov e r e d w ith silk by m eans o f
w hich th e tri a ngular ring a and through that and its
springs th e conductor co m m unicates w ith either the
e lectro m et e r or the electroscope
! uickly r a ising the conductor by pulling the cord f
the index o f the electro me te r w ill describ e a more or less
large i m pulsive arc a nd a fte r two oscill a tions w ill stop
a t the definit e a rc
H aving thus m easur e d the electric
te nsion of th e a ir and h a ving lo w ered the conductor I
next plac e the w ire i in co mmunicatio n w ith the elec
cer
tro s
c o p e B a nd by a g a in r a ising the conductor I a s
tain w heth e r the electricity be positive o r negative It
is scarc e ly necessary to sa y th at the conductor when
raised gives electricity o f th e sa me nature as th a t
prevailing at the m o m ent in the at mosph e re ; and when
low ered m a ni fests th e O pposite In so m e conj unctures
w e m ust keep tb e conductor raised and in c o mmunic a
tion w ith the e lectroscop e in order to obs e rve certain
pheno mena w hich I shall pr e sently d e scrib e : this method
I call observ a tion w ith a fix ed co nd ucto r
I have a lso constructed a si milar but portable
o r use o n eruptiv e cones w hen r e quired
a pp a ratus f
H avi ng giv e n this description of the a pparatus it
rem ains for m e to relate the r e sults obt a in e d especiall y
o n the occ a sio n o f the last e ruptio n o f Ves uv ius
The O bs e rv a tory is dista nt in a direct line fro m the
m etres so that when
central crate r o f Vesuvius
th e s m ok e is copio u s it is properly situated fo r the
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R E S U L T S O B TA I N E D F R O M
O B S E R VAT O R!
T HE
.
13 1
study o f electricity p a rticularly w he n the w ind incline s
th e pine tree cloud in the dir e ction o f the O bservator y
as frequently h a pp e ned on the l a st occasion
\Vith s m oke a lon e w itho u t ashes w e obtain e d strong
te nsions o f posi tive e l e ctricity w ith ashes only w hich
so m e ti m es fe ll while the s mok e turned in th e other
dire ction w e h a d stro ng negative electricity : w h e n the
s mok e inclined to w a rds the O bs e rv a tory a cco m panied
w ith a shes and l a pilli w e h a d so m eti me s o ne kind of
electricity and so m eti m e s the oth e r j ust as the s m oke
o r the a shes predo m inated ; a nd oft e n w ith a
fixed
conductor w e O bt a ined negative el e ctricity and w ith a
”
m ovabl e conductor
positive e lectricity In N aples
too at the Me t e orologic al O bs e rvatory attached to the
U niversity m y coll e a gu e P rofessor E ugenio S e mm o la
Observed neg a tive e l e ctricity o f stro ng tension w hilst
ash e s w er e falli ng th e re in abundanc e T h e tensions
on this occ a sio n w e r e so stro ng as to equal those
obtained at chang e s o f w eath e r o r duri ng stor m s
(temp o ra li) and b e ing b e yond m e asure w ith a d e lic a t e
e lectro m et e r w e m a rk e d the m w ith the sy m bo l OO
th e
sam e pheno me na w e r e observed w hen lightni ngs fl a shed
\Vh e n th e re is but lit tle s m ok e it is nec e ssary to
a pproach the e ruptive m ouths w ith a portabl e
appa
ratus in order to O bs e rve those pheno mena which
in great eruptions m a y be studied fro m the O bservatory
itself
The conditions unde r w hich (fo lg o ri) lightning fl a shes
are seen fro m th e cloud of s m ok e a re that it is con
1
e w ere
great
In
1
8
6
ther
v e yin
a bundance of ashes
g
sm all fl ashes ev e n fro m the line o f eccentric m outh s
,
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K
2
,
13 2
T HE
L AT E
E
RU PT I O N
o r V E SU V lU S
.
bove Torr e d el G reco a lthough th e s m oke w a s not
v e ry grea t ; a nd w h e n th e s e ceased to discharge and
the c e ntra l crater becam e so m e what active with a
m od e rat e a m ount o f s m oke but a great d e al o f ashes
s m all a n d frequ e n t lightni ng fl ashes w e re observed in
th e t w iligh t darting through the s m oke w hich w as
dark in colour
In 1 8 5 0 the e ruption w as m ore
vigorous the s m ok e m ore a bundant and the ashe s
sc a rc e b u t the fl a s hes w ere v e ry rare In 1 8 5 5 1 85 8
and 1 8 68 w ith a sc a nty su pply of a sh e s and a t int e r
v als no fl a sh e s w e re obs erved a nd the el e ctricity re
B ut having reg a rd to the
m a in e d const a n tly positiv e
fa cts of a nt e c e d e nt eruptions o ne s e e s th a t the fl ash es
a re a l w ays d e rived fro m th e m idst of s m oke a cco m panied
w it h a shes and lapilli w hich s e par a te lik e r a in fro m
the rol ling volu m e s o f s m ok e in the m idst o f which
they w e re ej e cted
B u t ho w c a n w e account for the positive electricity
o f the s m ok e a n d th e negative el e ctricity O f th e falling
a sh e s ? W ithout denying th e probability th a t a part of
the positive electricity d e pends u pon the e l e v a tion of
the s m ok e as in the case of every oth e r conductor w e
r aise aloft or w ith a je t of w a ter sent fro m a v e ssel by
co m pr e ss e d a ir I think th a t th e greate r part o f the
electricity proc e e ds fro m the rapid condens a tion of
v a pours w hich a re ch a nged fro m the g a seous condition
into d e ns e clouds ; for e v e n w hen th e s m ok e issues tr an
quilly a nd do e s not ri se b e c a us e carri e d a w ay hori
z o n ta lly by th e w in d it gives signs o f posi tive e lectricity
Fro m a ll m y studi e s o f at m o spheric e lectricity a nd fro m
so me e xpe ri m e nts m ade sp e ci ally it follo ws that the
a
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13 4
T HE
L AT E
E
RU P TI O N
0 F
V E S U VI U S
.
thunderbolts O f V e su v ius to b e harml e ss H o wev e r
if th e s m ok e w e r e v e ry gre a t and driven by th e force o f
the w ind to so me distanc e fro m th e cr a t e r w ith a n
it w ould b e possible to have
a bund a nt fall o f a sh e s
lightning fl a shes proce e d fro m th e s m ok e to th e e a rth
I poss e ss so m e docu m ents w hich r el a t e th a t in 1 63 1
thund e rbolts fe ll upon th e Church o f S anta Ma ri a d e l
A rco a nd oth e r pl a ces o n the coast of S orrento
A fter u p w ards O f t w enty years study an d O bserv a tion
o f m eteoric e l e c tricity I a m e n a bl e d to prove th a t a t m o
sph e ric electricity is nev e r m anifested w ithout rain h ail
and that m a nife sta tions o f light a re a l ways
o r sno w
acco mpanied by thund e r— m anife sta tions of light (la mp i)
thunder and rain b eing m ost clos e ly con nected W e m ay
h ave r ain w ithout m ani fe st a tions of light but never the
latte r w ithout rain o r h a il I c a nnot here r e p e at w hat I
have d e m onstrat e d in other m e m oirs I c an only say that
th e l ightnings o fVesuvius e rroneously b e li e ved to be not
acco m panied by thunder are r e ally not accom panied by
rai n but are induced by the descent of a shes and
lap illi (6)
,
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GE N E R A L CO N CLU S IO N S
WE
may conclude
.
fro m w hat I have stated :
That by the assiduous study o f the central crat e r
a nd
the indications afford e d by the Apparatus o f
”
V a ri a tions and the Electro Ma gnetic S eismo graph
w e c a n O btain precursory signals o f eruptions
and that
th e other pre monitory S igns pointed o u t by o u r
anc e stors such as the drying up of w ells either only
h a ppen o ccasionally o r are m er e coincidences such as
those of the coincidence o f a dry or a rainy season the
prevalence o f certain w inds etc *
2 That the fu m arol e s o f the lavas are c o m munic a
tions betw een the exte rnal surfa ce o f the lava hard e n e d
and m ore o r less cooled and the interior lava still p a sty
or at least incandescent
1
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,
“
”
-
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,
.
Earthqua ke s though in dista nt reg ions usu ally pre ced e e r uptions
T he Ea rthqu a ke of Melfi pre c e de d th e grea t E r uption of E tn a in
1 8 5 2 the Ea rthqu a k e of B silic t of D e c e mb e r 1 85 7 t ermin t e d
w ith the E r uption of 1 85 8 w hich fill e d the F oss a Gr a nd e w i th l a v
t he Ea rthqu a kes of Ca l a bri of 1 867 a nd 1 8 7 0 w e r e th e pr e cursors of
uvia n co nfl gra tio ns of 1 8 68 1 8 7 1 1 87 2 A V olca no lso
t he V es
in the I sl a nd of J a va ha d a grea t e ruption in the month of A pril
some days b e fore the la st c o nfl g r tio n of V e suvius asI lea rnt from
a l e tte r a ddre ss e d to S ig nor H e r e l S w iss Consul a t P a l e m o c m mu
e r S i nor Ca ccia tore — P a lmie i
by
tronom
h
nic a ted to me (
t
e
a
s
7)
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13 6
3
TII E
L
AT E
E
RU PT I O N
or
V E S U VI U S
.
Th a t fro m th e l a va w hil e flo wing there is no
esc a p e of a cid v a pours n e ith e r fro m the fum aroles a t the
first period of th e ir e xi ste nc e but th e s e if th e y l a st lo ng
e nough a rrive a t a n a cid p e riod
4
Th a t hydrochlo ric is the first acid that appears
co mbined a fter w a rds w ith sul phurous a cid a nd still
later w ith sulphurette d hydrogen
5 That v igorous lava stream s ma y have eruptive
fu maroles (S e e Translator s N ote 2 to p
6 That the subli m ations follo w a certai n order in
th eir appearance In th e neutra l period w e get sea s alt
mixed w ith so m e m etallic oxides the first of which is
oxide o f copper B ut in the great lav a s chloride of iron
a ppears si m ultaneously w ith the acid period
Hydro
chloric acid trans for ms the oxides into chlorides which
in their turn ch a nge into sulphurets or sulphates on the
a ppearance of sulphurous a cid
7 That the a cids by attacking the scori ae create ne w
chlorides and sulphates which are thus not products
m erely o f subli mation
8 That m icaceous peroxide O f iron — s
o co mmon and
abundant near the eruptive mouths— is very scarce and
rare on the lav a s unl e ss c o nveyed there fro m the
cr a ters
o m ani f
e st o n the fu ma
9 That chlorid e of iron — s
roles of the gr e at l a vas — is only fo und in s m all eruption s
close to the disch a rging mouths
1 0 That the frequ e ncy o f chloride o f iron in the
lav a s of great e ruptions m asks the ord e r o f transfor ma
tion of th e other products
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13 8
T
L AT E
HE
E
RU PTI O N O F V E S U VI U S
.
cov e r e d w ith s m ok e w hen look e d a t
sp e ctroscop e w ith d irect vi sion *
s m o ke giv e s positi v e e lectricity
falling a shes n e g a ti v e electricity
S
,
.
,
.
h v m de l rg coll ction
x minin g w ith th sp ctroscop nd
t h d is pos l of xp e rim nt lists w h
tions of this kind
I
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sublim t s w hich I purpos
bl to pl c som t
I s
h ll b
m y d sire to pursu e inve stig
a e
e a
a
a
e
e
,
e
a e
e a
a
T HE
R E F E R E N CE T O
P LAT E S
.
P LAT E
on of V suvius in 1 8 70 from P hotogr ph t k en
n r th O bs rv tory
T h A tri d l C v llo
b b F oss d ll V t n
Punt d l C ll
l L v of 1 8 5 8 n d 1 867
P olic B rr ck n r th O bs erv tory
j : P rt of Mont e S omm
Photogr ph f th O b se
I I A Profil of V suvius t k n from
t y in th month f S pt mb r 1 8 7 1
1 T h Cone on th 1 3 th J nu ry 1 8 7 1
2 2 L v of 1 8 7 1
bout t n
I I I A Profil of V suvius on th 1 6th A pril 1 8 72
d ys b fore th l st C nfl gr ti n
Photogr ph t k n
I V A V suvius on th e 2 6th A pril 1 8 7 2 from
in th n ighbourh ood of N pl s
1 T h O bs v tory
2 F oss d ll V t n
nd A sh e s w ith S ton s from th
3 E r ption of S mok
surf c of th L v
4
T h N ov ll S t S b sti no nd M ss
5 L v w hich took th dir ction f R s
in s
6 L v w hich from th Cr t e r took th dir ction of th
C m ldoli
7 T h G r in S tor s n r N pl e s
8 R sin
9 T orre d l G r co
1 0 T h C m ldoli
V A Pro fil e of V suvi s ft r th E ruption of th 2 6th A pril
Photogr ph t ken n r th O b s
1 8 7 2 from
T he C
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F ssur es of the 2 6th of A pril
S m a ll H ill thro w n up on the morning of the 2 6th of
A pril from b lo w w hich issu e d the grea t curre nt of
L va
4 4 4 T h e Mouths out of w hich the L a va issu ed
5 5 T he l a rg e r L a v a S tre a m w hich p a ss e d n e r the O h
s
e rv a t
y by the F oss a d e lla V et n a
S tre m w hich fte r dividi ng from
6 6 T h e oth e r L v
th e l st took the dir ction of R e sin a
7 7 T he L a va w hich an do w n tow a rds th C m ldoli
8 it 9 T he t w o Cr a t ers on th e summit O f th e Con e
V I A T he B ifilar E l e ctrom e t e r of S ignor Pa lmi e ri
(D eta ils)
V I I A T he a ss e mbl a ge of the E le c t O S CO pi A pp a r tus of S ignor
Pa lmie r i a sa rr nge d t the V e suvi n O bs erva tory
V I I I P rofe ssor P a lmieri sS e ismogra p hic A pp a r a tus
1, 1
2, 3
.
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14 2
T HE
L
ATE
RU PTI O N O F V E S U VI U S
E
.
ttr ct th eir a rm ture s w hich
conne cte d w ith l e ve rs T he
ction of 0 sl ve r is to stop th clock A w hich thus re cords to
h lf s cond the tim of th occurr nc
of th shock a t th s m
inst nt th t th clock strik s n al rm bell w hich ttra c ts th tt n
tion of n obse rv r T h l v r tt ch d to the a rm a ture of D t
th first inst nt of th e curr nt fr s th p e ndulum of the clock B
w hich w as b for e k pt from s w inging in a position out of t h
v rtic l the clock th n cts s time pi c e and its m otion
nrolls a b nd of p p er I I l t r t of thr m tre s n hour
A t th s m e tim e th
rm tur of D w hile ttr cted presse s p ncil
point g inst the b nd of p p r w hich p ss s ov r the roll r m
m rking on it whil e th r thqu k l sts s ri s of points or strok s
w hich occupy
l ngth of p p r corr sponding to its dur tion nd
w hich re cord the w ork of th shock
A ft e r it is ov e r the p p r con
tinn s to unroll from the dr m i nd p ssing round th clock rolls
on to the dr um l I f fr sh shock occur the pencil in dic t s it s
b fore on th p p e r nd th l ngth of bl nk p p r b et w n th t w
s ts of m rks is me sur of th int rv l of tim e be tw e n th
shocks B y w y of a ddition l ch ck s ver l h lic s h I k
hung
from st nd w i th sm ll p rm n nt m gn ts susp ende d from th ir
nds b lo w and close to th se l tt r e sm ll b sins holding iron
filin gs into th e s e the points of th m gn ts dip w h e n th eir h lic s
oscill te v ertic lly nd som filings r m in sticking to the m gn ts
s r cord of the shock
should r on it
O n of th m gn e ts h s
w hich mov s n ind x h and long
gr du a t d
a ssho w n in Fig 2
thus gain registeri ng the mount of th ve rtic l mov em ent Such
th
rr nge m ents i nt nd d for th r cord of the und ul tory or
hori ont l el em ents of the w v of shock
T h follow ing a th e rr ng m nts propos e d for re cording the hori
O n the st nd to th right of the clock A e s
z nt l motions
et four
ch p ir of
U sh p e d glass tub e s op n t th ir e nds
O ne of
tical branch e s must h ve di m et r t l st double th t of the oth r
T h se p airs w ith th eir suppor ting columns a e sho w n in pl n wh r
n
p ir lie s N and
noth r E nd W
third N E and
n d th e oth e r N VV
a nd S E
I t w ill b obs erve d th t m t llic b rs
p ss from the pilla r P ove r th nds f ll the long br nch es nd
simil r b a rs p ss f om R ov r th nds of the short branch es ; th
pill rs th ems lves s in th c s of t h oth r instrume nts a e e ch
conn cte d w i th o n pole of D ni ll s b tt ry the conn ctions
including the ele ctro m gn ts C nd D T h d e scription of o ne U
w ill pply to ll th oth rs
tub
n is p rtly fill d wi th m rcury
nd
n iron or pl tinum w ir
s sp nd d from th b a bove t h
short br nch d ips into the m rcury th r in w hil noth r pl tinum
w ir hung from th b
ov r th m outh of the longe r branch h s its
nd
ry close to the surf c of th m rcury in th t br nch A ny
sh ock w hich is not p rp endicul r in dir ction to the pla ne of th
br nch s of the U w ill c us th m m y to oscill t in th tub s nd
mor s nsibly in th a t w ith th sm ll r d i m e te r wh e n it ris s up in
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PRO F E SSOR
la tt
S EI S MO GR APH
’
P A L MI E R I S
14 3
.
so as to touch th platinu m point the conn ctio n b t w n
P nd R is m ad
n d th ci cuit com pl t d sta ti ng th actio n
f th
l ct o m agn ts 0 nd D w hich co d th shock as al ady d sc ib d
B y hav i ng th pl n s f th tub s st in th diff nt
is
m th s al ady
m ntio ne d n
mo
f th pai s is su
to b act d upo n nd by
obs ving in w hich th oscillation tak s plac th di c tion f th
shock is suppos d to b asc tain d B sid s this ach lo ng b a nch
i
f th U
that f sm all diam t has a sm all ivo y pull y 7
fi d above it ov w hich pass s a singl fib f silk w ith n i on
float at n
nd
sti ng n th su fac f t h m cu y t th oth
nd
f th fib
hangs a cou nt pois ; fi d to th pull y is a fin
i nd hand capabl f m ovi ng alo ng a g aduat d
W h n th
shock tak s plac th m cu y ising in th long b anch ais s th
float n its su fac t h silk fi b
at th sa m tim m ak s th pull y
volv w ith its i nd hand w hich aft w a ds m ain s statio na y
ast he cou nt
pois p vents th float f o m sinking agai n w i th t h
m cu y
T he
ading n th g aduat d
is thus a m asu f th
m ov m nts p oduc d in th i nst m nt by th ho i o ntal e l m n t f
th
shock nd is suppos d to m asu that sho k I t is ass m d
that in all th s i nst u m nts shocks h ow v s mall n b
co d d
w ith c tainty by adjusting th distan c e b t w n t h pl ti nu m poi nts
nd th m
cu y
T h a ang m n t f D ani ll s batt y u s d f th e s is m og aph is
show n in F ig 4 w h
conv ni nc f cl ani ng t h opp l
f
m nt is m ad
f wi
(about N o 8 B i mi ng ham w i gaug ) coil d
fl t w ithout t h spi als touchi ng
C ystals f sulphat
f copp
plac d at th botto m f th oute c ll into w hic h w at ispou d
nd th
i nn c ll into w hich th inc pl t go s is fill d w ith sili
cionssand
I n additio n to th abov e so me i ns t u m nts f a ough
d sc iptio n
em ploy d as ch cks
T hus at th foot f th pilla 0 th is a
w ood n t ough w ith ight hol s faci ng
sm any q uidista nt poin ts f
th com pass (
t w o f th m sho w n in s ctio n) ou nd its inne ci cu m
f e nc
m cu y is pou d i nto th basi n u n til its l v l is n a ly p to
th lips f th hol s
T h ef
f ct f a shock is to th o w so m e f th
nd th g
m cu y i nto n
f th s hol s
at th sil
mo
lation th m o m cu y is th o w n i nto th c lls th ough th hol s
f d a w ing ff th m cu y f o m th
T h sc w s sho w n outside
c lls w h n its q uantity n b m asu d T h di ctio n f th shock
is sho w n by s in g w hic h c lls
fill d w ith m cu y T his is th
old Cacciato e s i sm om t w hich has b n long m ploy d in I taly
nd D
b ny s
p
(S e 4 R po t f B itish A ssociatio n
cont ivanc F o m
V olcano s A pp ndix T h follo w i ng is an oth
hangs w i th a m tal ball at
th
m f th pilla G a fin m tal w i
mo
its nd which by its oscillatio n t h usts out n
light glass
t ub s st ho i ontally in a stand as sho w n in F ig 3 T h t w i ngs
sm all
nd t he glass tub s pass th ough hol s in th m
f w ood
l ath w ash s e plac d ou tsid the out ings th displ c m nt
th e
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a e
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14 4
TH E
LA
TE E RUPTI O N
VE S U V I U S
or
.
o tub s is ssum d to me su e th ho i ontal lem ent o f
f th e fi st shoc k
B y m ns f this ppa atus th tim
t h shock
is co d d as w ll as th int val b t w n th shocks nd the du a
ho i ontal is giv n
tion f ach 3 th i di ctio n w h th ve tical
as also th m a imu m f int nsity P of sso Pal mi i has th inst u
am in d th e tim s a day nd n ssistant obs v is al w ays
m nts
at b and to att nd to th b ll nd put back the appa atus to its
no m al positio n f f sh obs v tion
I t has b n stat d that this inst u m nt is sensi b l to m os t f the
shocks w hich occu in the M dit an an b sin
n
I t is n t my i nt ntion h to off ny c iticis m s to th
st ction
p fo m anc s f this inst u m nt th ath as I m us t
co nf ss I do n t q uit sha th high pinion f its inv nto as to th
c tainty
actitud f its in dications
Th
t m i mpo tanc to sci n ce
n b n
q u e stio n as to th
stablish m nt nd con tinu d s f s ism og aphic inst
f th
m nt
const uction at th O bs ato y pon
f u n c ption abl
V suvius nd it w ould b a valuabl gi ft to sci nc w th I talian
n
G ov n m nt to nabl
S ig no Palmi i to stablish such n
I ts g at valu n d th v y fi s t p obl m to st th in st u m nt to
ig id d t m in ti n f th d i
ti n f p p
solv should b by
st o ng pulsatio ns
h k f th os sligh t
g ti n f th w
of s
w hich p c d
acco m pany th V suvian lik ll o th
uptions
n a
iti n
ivi ng at th O bs vato y t fix th d p th nd th p s
ti lly b n
th s p u lss
d i d
This
th th
n
wh n
w oul d b
in f ct to fi th d p th n d posi tion b n ath th m ou ntain
at w hich th volcan ic focus is situa t d f th ti m
at l ast
wh
th
volc nic activity is at th ti m g at st A nd th
ass d kn o w l dg v n w ithin m od at li m its f accu acy f this
d pth nd v n f this si ngl m oun tain w ould b n i mm n s
acc ssion to
positiv k no w l dg nd a ally n w st g g ain d
f futu
advanc s At p s nt w k no w but littl sto th actual
d pth b lo w
glob s su fac t w hich volca nic activity occu s
to w hich it is lim it d ith up w a ds dow nw a ds I hav m ys lf
stablish d som data upon th flan ks f E tna n t y t publish d
w hich m y n abl m to ffo d som i nfo m ation n th subj ct h
aft
M an w hil P of sso P al m i i poss ss s u n ivall d pp r
t niti sf
such hs ti ns; nd I t ust h alth lif nd m ans
m y b affo d d him to b co m th fi st w h shall hav m ad this
g at addition to
positiv kn o wl d g f V ulcanology
S f
pop la ly at l ast th all g d chi f u s s nd valu f th s e
s ism og phic i nst u m nts at th O bs vato y f V suvius h av
b n m ad to d p n d upon th i b i ng p sum d t ffo d m ans f
fo t llin g
uptio ns
affo ding p cu so y w a ni ngs f th i p
babl p og ss n d d st uctiv cou s
I f l co mp ll d to e p ss m y wn total disb li f in th possibility
f ny such p dictio ns in th p s n t s
tat f sci nc by th h lp f
fs
uch a natu r as to b e o f any p
any i nst uments whatso eve
m
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ra c
14 6
L AT E
T HE
E
RU PTI O N O F
s
v n uv w
s
.
issuing bove the mouth T his w s vide nt in th disch rg s issu ing
in 1 8 5 7 fro m the highly instructiv m ino bo c the n m it ng
x min d by me and efe e d to R port N ple s E arthqu k s, t
V l I I pp 3 13
spr s nting t t h e tim gr e t f c il iti s for
d t rmining pyrom tric lly the t mp r ture o f the l v W ith in nd
of the d y sup rheate d st m issuing w ith a rhythmi c ro r from t
M L C q E p q ues G é ologiqu s d A u e g ne T ome I V ) h s e
cord d som e e x mpl e s of the form tion a nd p ning t of l rge
bubbl lik c viti s in l v lr dy j cte d Pe rha ps th t bl nd
l borious vulcanologist whos d th f w months g sci enc still
d plor s ttribute s too much im port nc e asw e ll s m gnitud to
th m w hen a ttri buting the form tion of w ha t h has d nomi n te d
cr t rs of e xplosion t the m ch nism of the ris e and bursting of
such bubbl s upon a gig ntic sc l S uch blo w ingsforth sudd n or
prolong d from p rticul r spots of l v streams en o u t undoubt dly
m y lso h v th e ir origin in d mp pl c s or w a t e r or a i fill d c v it s
in or b n th the b e d over w hi ch the l va rolls w hich ge tting gr du lly
h t d g n rate st m or ai or g s s under tension by e xpansion tc
w hich thus t l ngth blo w through th liquid or p sty l v
flow ing
bov nd w hich in bursting through d livers much dust lso nd so
simul t s a littl e ruptive cr t r E x mple s of this upon gr t
nd convincing sc l e c an b e point d to in the V l di C l nn
nd
ls wh r on Etn a
a
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.
T h e re a e strong grounds for the grav est doubts tha t
th re e xists a ny re a l connection of a physica l cha racte r be t we e n
V olc a nic E ruptions and E a r thqu k e s mor e or l e ss appro xim a tely coin
c id e n t onl y in tim e of occurrenc e
th e re sp e ctive sit e s b e in g w id ly
p rt and the le ss the proba bility sthe interve ning dista nce is gre a te r
T he discussions of the l a rge numb r of r e cordstha t a re to b fo u nd
of such coincide nc e s — mostly but p a rti l and in but v ery fe w in
stan ce s comple te coincide nce s— b y Pe rrey von H 0 13 , a nd oth ers s
w e ll a sby mys e lf do not t e nd to sust in the V ie w th a t such imp e rf ct
conte mpora neity is ba se d upon a ny c usa tive connection T h se ismic
reg ion of Gre ec e a pp ears to h a v no d irect connection w ith tha t of
S outh e rn I t ly : the b and of conn e ction if a ny see ms to lie b e tw e e n
N orth e rn I ta ly a cross the N orth e rn A dria tic by R agusa a nd the nc e
spre a ding into A sia Minor
r
.
e
a
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'
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.
(P
bundanc of col opt r a nd of v rious oth r
forms of ins ct life a b out l v b ds both re ce nt and old is a v ry
singul r f ct and ne w orthy of the c r ful observa tion of nt m l
gists I n the a utumn of 1 8 64 t mid d y w h e n sitting sk tching
upo n th l va a bout the middl of the V al d el B ove (E tn ) I found
it l most impossibl to w ork or v n to re m in for an inst nt still in
cons que nc of the continu al cloud of insects la rge and sm ll th t
struck g inst m e in flight nd ange r d th e ye s a nd s wa rm d upon
4
T he
.
a
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a
T HE
CR O CE LLA
14 7
.
my cloth e s I t is quit possibl th t this loc l sup e r b nd nc of
i ns ct li f m y ris m r ly from th ge n r l dryn ss nd w rmth of
such pl c s nd th pl ntiful mld u sth t th innum r bl c viti s in
l v fford f th ggs nd rli r st g s of inse ct lif still thi s
pp rition of n form of lif m y lso b e conn ct d w ith oth r cir
u ms
t n e snot unimport nt to discov r
e
.
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is sm ll w ood n cross r ct d s v r l
y rs g nd w hich n p ss s to th right h nd t the upp r
nd of th
p th lo ng th ridg of tuf nd volc nic ng l m
r t upon w hich the O bs rv tory st nds in sc ndi ng th nc to th
A tri d l C vallo
5
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T ha t the c a us e s a ssigne d by P rofe ssor Pa lmie ri for
positive or ne ga tive ) w hich
the pot e nt d e v e lopm e nts of e l e ctricity (
chara ct e rise the a sc e nt of the issuing columns of (chi e fly if no t a l wa ys)
d y stea m w ith a re l tiv e ly sm a ll volum e of v a rious ga s e s a n d
thro w ing up in th eir bla st volume s of sma ll solid p a rticle s in a sh e s
a nd the subs e qu e nt fa ll a s a min e ra l or stony h a il
a n d l a pilli e tc
show e r of the la tte r thro ugh the pa rti lly conde nsing va pours and
the circuma mbie nt a i a e the ma in ca us e s of l ectric a l d e v e lopme nt
e vid e ncing its e lf in lightn ing fla sh e s is no doubt t r
u e We m ust
not how e v r lose sight of the ma ny oth e r and ve ry e ffective a ge ncie s
T he a ctu a l bocca of
t w ork h e re to produc e e l e ctric e x cit e me nt
f constitut e the con e
the volc a nic v e nt w h e nc e the st ea m ro a rs o f
veri ta ble hyd ro e le ctric m a chine M e cha nica l e ne rgy in va rious
forms is transforme d into e le ctric e ne rgy Che mica l a ction isgoing
on both in the solid a nd in the va pourous a nd ga se ous e mana tions s
the y rush into nd rema in in the ai or d e sce nd from it a nd ch emical
me d in p rt into e l e ctric n e rgy P rcussion b etw e e n
a ction is tra nsf
de sce nding p article s a nd fra gm ents fr cture s a nd
a sce nding
a nd
bre aking up of more or l e ss of th e se thus nd by sudd e n change s
of t e mp era ture in cooling a e like w ise op e ra tive I n a ddition
r
t
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mov
e m e nts in the a tmosph e re its e lf r e sul t fr om
ea
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g
the l rge loc a l ac c e ssions of t e mp e r tur e by the h ea t e d volume drive n
up into it a nd w hich in turn g ive rise to e le ctric disturba nc of
t he sa m e cha r a ct e r a s thos e produc e d in w ind storms a n d w hirl
w inds brought a bout by the n tura l c aus e s w hich e v e ry d a y e ffe ct
disturba nc e s in our a tmosph e re ll ove r the globe
6
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(
H o w is it possibl e in the pre se nt st a t of
b e re fe rr e d to a sin point
scie nce a t l e st to st blish ny physic l conn e ction b etw e e n an crup
tion in J v n d ne of V suvius w ith h lf th w orld be t we n w h n
solita ry conn cting link of comple te contempo
n o t e v n h a ving th
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14 8
L AT E
T HE
RU PTI O N
E
or
V E S U VI U S
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hich if it e x ist d y t might b e nothin g but a ccid nt l ?
A list of s ocks upon r e cord w hich h
occurre d mor or l e ss n rly
simult n ously t dist n t p rts of th w orld m y b e found in my
fourth R port Fa cts
of E rthqu k s B ritish A ssoci tion R ports
1 85 8
nd the r
sonsa e th r giv n for eje ting the notion of ny
dir ct physic l conne ction b tw n the originsof the re sp ectiv shocks
S hocks man a ting from th l s n ighbourhood of volca nic
nts
or simult ne ity of e ruption in v nts n t f dist nt from e ch oth r
st n d pon differe nt footing
d w
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