Surviving Apparatus Showing the Early Development of the
Cloud Chamber
Tacye Phillipson
Morning after morning I saw the sun rise
above a sea of clouds and the shadow of
the hill on the clouds below surrounded
by gorgeous coloured rings. The beauty
of what I saw made me fall in love with
clouds and I made up my mind to make
experiments to learn more about them.
C.T.R. Wilson, Nobel banquet speech, 1927
The cloud chamber, the first device to
make visible the paths of rays and particles of radiation, is a very significant piece
of apparatus for the development of early
20th century physics. Its history has been
extensively documented1 and in this paper
I will place a few surviving artefacts into
the framework of this history, adding to and
providing material support for the narrative, and giving a more detailed perspective
on these instruments.
The history of the cloud chamber usually
starts on the top of Ben Nevis, where in
September 1894 a recent physics graduate,
one C.T.R. Wilson (Charles Thomson Rees
Wilson 1859-1969), spent a fortnight as a
volunteer taking observations as a relief to
the regular staff at the meteorological observatory. Wilson himself describes how
the beautiful optical phenomena, such as
the coronas and glories, that he saw in the
clouds on Ben Nevis inspired him to start
work investigating clouds in the laboratory.
For this he turned to the work of another
Scottish scientist, John Aitken, who had
demonstrated that clouds and fog formed
when moisture in the air condensed onto
minute particles of dust. Aitken used this
condensation, which he triggered by expansion of the moist air, in the invention
of his dust-counter and koniscope, both of
which made clouds in glass and brass vessels.2
Aitken was interested in dust particles and
their effect on both human health and the
weather: concerns which are still current
today. Two versions of Aitken’s dust counter formed part of the equipment of the
Ben Nevis meteorological observatory: a
large fixed apparatus indoors (with air sampled from outside); and a smaller portable
apparatus which could be set up outdoors,
when the weather permitted. Regular observations were taken with these, counting the number of condensation droplets
formed on nuclei from a measured volume
of sampled air, and the results correlated
with weather conditions and visibility.3
The dust-counter precipitated a portion of
the cloud onto a glass slide, and the water
droplets were counted with a magnifier.
It was assumed that the entire cloud in a
column above the slide had precipitated
downwards and the count was converted
into number of particles per volume of air.
To achieve a countable number of drops on
the slide the sample air was diluted with a
portion of filtered air. An example of Aitken’s pocket dust counter featured as the
mystery instrument number 1 in the September 2016 issue of this Bulletin, and another one is found in the collections of the
Science Museum, London.
In addition to these qualitative dust counters,Aitken devised in 1892 a simpler quantitative instrument to indicate the amount
of dust present in air. He called this instrument a ‘koniscope’, and it too works by
triggering condensation with the expansion of moist air.4 The koniscope consists
of a brass tube with glass windows at either
end. When in use it was lined on the inside with moist blotting paper. At one end
this is linked to a graduated piston pump,
at the other a stopcock admits the air to be
sampled. The density of fine water droplets was estimated by eye looking along the
tube in which the cloud had been formed,
the perceived depth of colour increasing
with the amount of fine particles present.
Relatively few references to the use of this
instrument by people other than the inventor survive, which is an indication that
there may not have been many examples
made. In The Air of the New York Subway
Prior to 19065, George Soper refers to importing a koniscope from Glasgow to estimate the number of dust particles in the
air, having tried Aitken’s ‘more elegant and
exact’ dust counter and found it required
more delicate adjustment and better light
than was available in the circumstances.
A koniscope was presented to the National Museums Scotland by the Scottish
Meteorological Society on permanent loan
in 1972, and formally transferred in 1983.
This instrument was made in Edinburgh by
William Hume.6 It is documented as having
come from the Ben Nevis observatory, but
must have been in addition to the two dust
counters, which were well documented. It
is still tempting to speculate that C.T.R.Wilson may have encountered this instrument
as well as the more elaborate dust counters
during his time at the observatory (Fig. 1).
Bulletin of the Scientific Instrument Society No. 131 (2016)
Fig. 1 Koniscope, a qualitative
measurer of atmospheric
particles, invented by John
Aitken and made by William
Hume of Edinburgh, c. 1892
(Photo: National Museums
Scotland).
From 1895, C.T.R. Wilson researched the
formation of clouds of condensation and
devised apparatus in which to form and
study these at the Cavendish Laboratory
at the University of Cambridge. His initial
apparatus was based on Aitken’s dust counter7; however, he developed this to give
a more sudden expansion, by means of a
piston made of ground and blown glass.
Wilson demonstrated that under certain
conditions it was possible to trigger condensation in the absence of dust particles,
and deduced that the droplets formed on
positive or negative ions.8 This was a useful
tool for studying the ions themselves, as the
number of droplets, and the electric charge
on each droplet, could be related directly
to the ions.
The exact design of the expansion apparatus used progresses between the papers in
which it is described.9 In its first appearance in 1897, the piston is 3 cm long and
2cm wide. Two slightly larger versions are
described as breaking on almost the first
use, and ‘more than one’ jammed fast. Later
papers show the apparatus was changed
so the piston struck on expansion against a
rubber bung, rather than on a constriction
of the outer glass tube, and the top of the
tube was variously blown to form the experimental chamber or constricted to take
tubing linking it to the experimental chamber. The dimensions of the piston are not
given in the later papers, but the diagrams
give an idea of its size, which was about
4cm in diameter.
Professor J.J. Thomson remembered10 ‘For
many years he [Wilson] did all the glass35
In 1903 Harold A. Wilson 1876-1964 (who
was no relation to C.T.R. Wilson, and not
the Prime Minister) used this phenomenon of condensation on ions to measure
the charge of an electron. In a forerunner
to Millikan’s famous oil drop experiment
he observed the top of the condensation
cloud as it fell between two horizontal metal plates and how this was affected by an
electrical potential between these plates.
For this he used an expansion apparatus
‘kindly lent to me by Mr. C.T. R. Wilson’.12
In 1905 Harold Wilson moved to KCL
where he remained as professor of physics
until 1909, and it is extremely tempting to
associate with him this apparatus, which
appears appropriate for carrying out this
experiment. Perhaps the borrowed apparatus was never returned.This apparatus consists of a wooden tripod supporting a large
glass piston in a glass cylinder. The bottom
bung is pierced for a tube which would
have led to an evacuated vessel. Mounted
on top of the cylinder is a smaller glass cylinder, the experimental chamber. This contains two parallel horizontal plates, there
are electrical contacts top and bottom, and
an outlet tube to admit the gas which was
to be expanded. The piston cylinder is sup-
ported between three rods with threaded
ends, similarly to the Cavendish example.
The Cavendish example is constructed of
glass with sealing wax joining the tubes13,
while the KCL apparatus has rubber tubing
at the joins between glass tubes.
In 190414 C.T.R. Wilson used a cloud chamber which replaced the glass piston with a
larger brass one, 10 cm in diameter and 30
cm long. This apparatus was made by W.G.
Pye and Co. and is an intermediate step towards the 1912 version of the cloud chamber which made particle tracks visible and
also had a brass piston.15 W.G. Pye had been
superintendent of Cavendish workshops
until 1899.16
While the majority of the published research utilising Wilson’s expansion apparatus originated from the Cavendish Laboratory, one exception originated from the
Chemical Laboratory, University College,
London, where F.G. Donnan worked on
condensation in 1901.17 Either this apparatus had been provided by C.T.R. Wilson, or
the expertise to duplicate it was available
in other laboratories.
In 1911 C.T.R. Wilson published the first
images of particle trails taken in a cloud
Fig. 2 Cloud chamber expansion
apparatus from King’s College London,
c.1903 (Photo: National Museums
Scotland).
blowing himself, and only those who have
tried it know how exasperating glass-blowing can be, and how often when the apparatus is all but finished it breaks […] Old research students when revisiting the Laboratory would say that many things had altered
since they went away but the thing that
most vividly brought back old reminiscences was to see C.T.R. glass-blowing.’ Wilson
was later assisted particularly by the technician George Crowe who had joined the
laboratory as a boy in 1907 and to whom
he had taught glassblowing.11 Crowe was
strongly associated with the manufacture
and design of later cloud chambers, he later
became Rutherford’s personal assistant.
A ‘cloud chamber condensation apparatus’
(Fig. 2) which has been on loan to National Museums Scotland from King’s College
London (KCL) since 1951, belongs to this
series of designs and is extremely similar
to the 1899 example which survives at the
Cavendish Laboratory. Is this another example made by C.T.R. Wilson, or was he not
the sole maker of these expansion chambers? How did it come to be at KCL?
36
Fig. 3 One of the first commercial batch of six cloud chambers23, CSI, 1913 (Photo:
National Museums Scotland).
Bulletin of the Scientific Instrument Society No. 131 (2016)
this model.22
The cloud chamber is of unquestioned significance in the history of particle physics.
These surviving artefacts enhance the story
of C.T.R.Wilson's long, progressive development of this apparatus.
Notes and References
1. For instance in: P. Galison and A. Assmu,
‘Artificial Clouds, Real Particles’ in D. Gooding, T. Pinch and S. Schaffer, eds, ‘The Uses
of Experiment: Studies in the Natural Sciences (Cambridge, 1989), pp. 225-274; C.
Chaloner, ‘The Most Wonderful Experiment
in the World: a history of the cloud chamber’, The British Journal for the History of
Science, 30 (3) (1997), pp. 357–374 and S. L
Barron, C.T.R.Wilson and the Cloud Chamber (Cambridge, 1952).
2. C.G. Knott, ed., Collected Scientific Papers of John Aitken, LL.D., F.R.S. (Cambridge, 1923).
3. A. Rankin ‘Dust Counting on Ben Nevis’,
Nature, 45 (1892), pp. 582-584.
4. Aitken, op. cit. note 2, pp. 280-283.
5. George A Soper, ‘The Air of the New York
Subway Prior to 1906’, Technology quarterly and proceedings of the Society of
Arts, 20 (1907), pp. 108-116
Fig. 4 Schools’ model of cloud chamber, CSI, 1925 (Photo: National Museums Scotland).
chamber and revolutionised particle physics.18 He had developed his apparatus
to such sensitivity that the formation of
clouds could be confined to the immediate
location of ions formed by the passage of a
charged particle through the chamber. This
was the first time the paths taken by particles could be observed. This cloud chamber also survives at the Cavendish Laboratory, and C.T.R. Wilson is documented as
assuring Sir Lawrence Bragg when he was
setting up the Cavendish historical collection ‘But I never made but the one!’19
The Cambridge Scientific Instruments
Company (CSI) worked with Wilson to produce in 1913 a commercial batch of six of
these instruments, two of which are known
to survive.20 The one now at National Museums Scotland is sadly missing the upper
glass cover and was used at the University
of Edinburgh (Fig. 3). While W.G. Pye and
Co. had assisted in the manufacture of the
1904 apparatus it was CSI who produced
the commercial models. According to Cattermole and Wolfe’s history of the company21 it was CSI who approached Wilson to
request the collaboration, they themselves
having been approached by other scientists
wishing to purchase cloud chambers.
The association between the CSI and the
manufacture of cloud chambers continued
as the instrument was developed. In 1921
a graduate student at the Cavendish Laboratory, Takeo Shimizu, developed a cloud
chamber with repeated expansions which
could be coordinated with an automatic
camera and allow many more particle
tracks to be photographed, to enable rare
events to be recorded; this was the beginning of the huge amounts of data gathered
for particle physics. The CSI manufactured
research cloud chambers of Shimizu’s design, but also developed and made a reliable student model, which operated by a
turn handle and brought the cloud chamber into teaching and outreach. Two of
these were subject to very heavy use at the
Festival of Britain in 1951 by an estimated
3000 people a day for five months. The
example of this model in the museum collection has serial number C72755 (Fig. 4)
which according to the company records
at the Whipple Museum was issued as part
of a batch of 20 ‘Ray-Track Apparatus’ on
the 13th of October 1925. This predates the
usually given dates for the introduction of
Bulletin of the Scientific Instrument Society No. 131 (2016)
Another reference is E.V. Hill ‘Quantitative
Determination of Air Dust’, Heating Ventilating Magazine, 14 (1917), pp. 23–33.
6. T.N. Clarke, A.D. Morrison-Low and A.D.C.
Simpson, Brass and Glass (Edinburgh,
1989), p. 133.
7. C.T.R. Wilson, ‘The Formation of Cloud
in the Absence of Dust’, Proc. Camb. Phil
Soc. 8 (1895), p. 306 is a brief 2/3 page note
with no references which mentions ‘The
cloud-formation is brought about as in the
experiments of Aitken and others’. C.T.R.
Wilson, ‘Condensation of Water Vapour in
the Presence of Dust-free Air and other
Gases’, Proc. R. Soc. 61 (1897), pp. 240-242.
8. C.T.R. Wilson (1897), op. cit. note 7.
9. M.J.G. Cattermole & A.F. Wolfe, Horace
Darwin’s Shop (Bristol, 1987) says he
‘made about 3’ useable cloud chambers (p.
252). This may have referred to just 1895
as considerably more than three different
examples are evidenced by the surviving papers over the first ten years of the
cloud chamber’s history. See for example
C.T.R. Wilson (1897), op. cit. note 7; H.A.
Wilson, ‘A Determination of the Charge on
the Ions produced in Air by Röntgen Rays’,
Phil. Mag, Series 6, 5 (1903); J.J. Thomson,
‘On the Charge of Electricity carried by the
Ions produced by Röntgen Rays.’, Phil. Mag.
37