1920-21.] 
Meetings of the Society. 
217 
ELEVENTH ORDINARY MEETING. 
Monday , July 4, 1921. 
Professor Frederick 0. Bower, M.A., D.Sc., LL.D., F.R.S., F.L.S., President, in the Chair. 
A Ballot was taken for election to the Honorary Fellowship of the Society. Dr H. S. Allen 
and Dr G. A. Carse were nominated as Scrutineers and the undernoted gentlemen were declared 
duly elected to the Honorary Fellowship : — 
British Honorary Fellows. 
Foreign Honorary Fellows. 
William Henry Perkin. 
Sir Ronald Ross. 
Sir Ernest Rutherford. 
Sir Jethro J. H. Teall. 
Reginald Aldworth Daly. 
Johan Hjort. 
Charles Louis Alphonse Laveran. 
Heike Kamerlingh Onnes. 
Salvatore Pincherle. 
Dr T. M. MacRobert and Mr Wm. Arthur signed the Roll and were admitted as Ordinary 
Fellows of the Society. 
The President announced the awards of the Gunning Victoria Jubilee and Makdougall-Brisbane 
Prizes, in the following terms, and presented the Prizes. 
The Gunning Victoria Jubilee Prize is awarded to Mr C. T. R. Wilson, F. R.S., in recognition 
of his important discoveries in relation to Condensation Nuclei, Ionisation of Gases, and Atmo- 
spheric Electricity. 
Mr Wilson’s first group of important contributions to science {Phil. Trams., vol. clxxxix, 
1897 : vol. cxciii, 1899) related to Condensation Nuclei, a subject which had been initiated by 
our distinguished Fellow — Dr John Aitken. He discovered the existence of two definite limits 
to the supersaturation in moist dust-free gases, a lower limit beyond which rain-like condensation 
occurs, and an upper limit beyond which cloud-like condensation occurs. He showed that nuclei 
identical with those which give rise to the rain-like condensation are produced in great numbers 
by X-rays and other agents which give conducting power to a gas ; and proved that such nuclei 
are removed by an electric field and are therefore identical with the charged “ions” to which the 
conducting power of the gas is due. This discovery furnished much more direct evidence than 
any previously available for the existence of discrete “ions,” each individual ion being made 
visible by the condensation of water upon it. The earliest determinations of the charge carried 
by an ion were made by J. J. Thomson and H. A. Wilson by applying this method. 
Mr Wilson’s next group of researches (Camb. Phil. Soc. Proc., 1900-1902; Proc. Roy. 
Soc., vol. lxviii, 1901 ; vol. lxix, 1902) related to the natural ionisation of gases. He showed 
that air and other gases conduct electricity to a minute extent under normal conditions, even 
when dust-free and contained in closed vessels. This conduction he proved to be due to the 
continual production of ions, the number produced per sec. being determined. The method 
introduced for the purpose of this investigation has since been extensively used in radio-active and 
similar work. 
After this Mr Wilson’s attention was turned to Atmospheric Electricity (Camb. Phil. Soc. 
Proc., vol. xiii, 1905-06; Proc. Roy. Soc., vol. lxxx, 1908). He devised a new method for 
measuring the surface charge on the ground (and hence the vertical electric force) and at the 
same time determined directly the current from the atmosphere into the ground. These experi- 
ments, which were made at Peebles, gave the first direct measures of this current. 
In 1911-1912 (Proc. Roy. Soc., vol. lxxxv, 1911 ; vol. lxxxvii, 1912) he published important 
work on the Tracks of Ionising Particles. The expansion apparatus of the earlier condensation 
experiments was modified so that the ions were made visible as minute drops and photographed 
in the position which they occupied immediately after their liberation. The tracks of the indivi- 
dual alpha and beta rays from radium and its products, and of the electrons emitted in air when 
exposed to X-rays, were thus made visible. In the case of the fast /3-rays the individual ions 
liberated along the track of the corpuscle are made visible in the photographs. This work made 
clear the nature of the ionisation of a gas by X-rays, viz., that it consists in the ejection, from 
the atoms of the gas, of electrons, each of which ionises the gas along the course of its flight. 
In more recent years Mr Wilson has published further researches in Atmospheric Electricity 
and Thunderstorms {Proc. Roy. Soc., vol. xcii, 1916; Phil. Trans., vol. ccxxi, 1920). The 
method of measuring the surface charge on the ground was modified so as to allow of automatic 
records being obtained, a special type of capillary electrometer being devised for the purpose of 
measuring charges. This was applied to study the variations in the electric field during thunder- 
storms, including the sudden changes produced by the passage of lightning flashes at various 
distances. The “electric moments” of a large number of flashes were thus measured, and 
estimates obtained of the quantity of electricity which passes in a flash. The results of these 
observations have been applied to the Theory of Thunderstorms. 
