BY THE ACTION OF A RADIO-ACTIVE SUBSTANCE, ETC. 
277 
diffusion show plainly that the sizes of the ions produced by point discharges vary 
with the arrangement of the apparatus in the neighbourhood of the point. What is 
necessary in order to come to a definite conclusion with regard to the charges is to 
examine the coefficients of diffusion and the velocities of ions produced under similar 
circumstances. This would be possible with the apparatus I have used for the deter¬ 
mination of the coefficients of diffusion, and I hope to be able to make observations 
on the velocities which will lead to an accurate determination of Nr. 
This method of obtaining the charge on an ion in a gas in terms of the charge on 
an ion in a liquid electrolyte is of some importance, as it enables us to obtain 
evidence of the atomic nature of electricity. 
The results show that there is a similarity between the minimum subdivisions of 
electric charge in liquids and in gases. 
The methods hitherto used for the determination of the charge in absolute units 
apply to ions produced in moist gases, and since all the determinations depend upon 
the rate at which a cloud falls, great accuracy cannot be expected. The results show 
that the charge on the carrier is of the same order for ions obtained by various 
methods. The charges have been obtained by Professor J. J. Thomson for ions 
produced by Rdntgen rays,* * * § and by ultra-violet light ;t the values are nearly the 
same, being between 6 x 10 -10 and 7 X 1 0 —1 1 electrostatic unit. These values do 
not differ very much from the value 5 X 10 -10 which I obtained for the charge on the 
carrier in the charged gases given off by electrolysis, j 
If we consider that the charge is the same in all cases, we must assume that the 
mass surrounding the ion varies in order to account for the differences observed in the 
coefficients of diffusion. McClelland,^ by examining the velocities of the ions 
produced by an arc and by glowing wires, found that the mass attached to the ion 
depends to a great measure on circumstances connected with the ionization. The 
velocities undergo large changes for small differences of temperature of the wire, 
showing that the mass which collects round an ion is very variable. We would not 
expect that Pontgen rays or radio-active substances would have an effect upon the 
air, which would alter its tendency to collect round a charged ion, but it is possible 
that ionization is produced in different ways by different kinds of rays, so that the 
masses are not identical. With point discharges in air there are actions taking- 
place which would tend to make the carrier increase in size. Thus the oxides of 
nitrogen which are formed might condense round the charge and lower the rate of 
diffusion hy increasing the mass of the ion. 
It is uncertain whether ultra-violet light has any effect on dry air, but Wilson|| 
* J. J. Thomson, 1 Phil. Mag.,’ Dec., 1898. 
t J. J. Thomson, ‘ Phil. Mag.,’ Dec., 1899. 
} J. S. Townsend, ‘Phil. Mag.,’ Feb., 1898. 
§ J. A. McClelland, ‘Camb. Phil. Soc. Proc.,’ vol. 10, Part VI. 
|| C. T. R. Wilson, ‘ Phil. Trans.,’ A, vol. 192, 1899. 
