[ 25 ] 
11 . Energy of Ron tgen and Becqnerel Rays, and the Energy required to 
produce an Ion in Gases. 
By E. Eutherford, M.A., B.Sc., Macdonald Brofessov of Physics, a,nd E. K. 
McClung, B. a., Demonstrator in Physics, McGill University, Montreal. 
Communicated hy Professor J. J. Thomson, F.R.S. 
Received Jmie 15,—Read June 21, 1900. 
The primary object of the investigations descril3ed in this paper was the determination 
of the amount of energy required to produce a gaseous ion when Ebntgen rays pass 
through a gas, and to deduce from it the energy of the radiation emitted per second 
hy uranium, thorium, and other radio-active suhstances. In order to determine the 
“ ionic energy ” (as it will be termed for brevity), it has been necessary to make 
a special investigation to measure accurately the heating effect of X rays when the 
rays are absorbed in metals, and also the absorption of the rays in gases. 
The method employed to determine the ionic energy was briefly as follows :—The 
total energy of the rays emitted per second was determined by measuring the heating 
effect of a knovni proportion of the rays when absorbed in a metal. The total number 
of ions produced by complete absorption of the rays in the gas was deduced from 
measurements on the current produced by the ionization of a known volume of the gas 
and of the absorption of the rays in the gas, assuming the value of the ionic charge 
recently determined by J. J. Thomson. 
On the assumption that all the energy of the X rays is absorbed in producing ions 
in the gas, the total energy of the rays, divided by the total number of ions produced, 
is a measure of the energy required to produce an ion. 
In the course of the investigation the following subjects have been considered :—■ 
(1.) Measurement of the heating effect of X rays and the total energy of the rays 
emitted per second. 
(2.) Efficiency of a fluorescent screen excited by X rays as a source of light. 
(3.) Absorption of X rays in gases at different pressures. 
(4.) Energy required to produce an ion in gases, with deductions on— 
(a.) Distance apart of the charges of ions in a molecule. 
(6.) Minimum potential required to produce a spark m the gases. 
(5.) Eate of emission of energy from the radio-active substances, uranium, thorium, 
radium, and polonium. 
VOL. cxcvi.— A 275. 
E 
27.2.1901. 
