ox ENERGY OF RONTGEN AND BECQUEREL RAY^S, ETC. 
53 
Energy of Radiation of Radio-active Substances. 
In a previous paper it has been shown that tlie ions produced in air l:)y uranium 
radiation have the same velocity as the ions produced by Rontgen rays. On the 
assumption that the same amount of energy is required to produce the ions, whether 
the agency is Rontgen or uranium rays, the energy of the radiation given out into 
the gas can be at once determined. Fig. 7 shows the arrangement of the apparatus 
to determine the current through air produced Iry the uranium rays. 
Two large parallel plates, A and B, 4‘1 centims. apart, were insulated from each 
other. A was connected to the electrometer in the usual manner, and B was con¬ 
nected to one pole of a battery of small cells of 310 volts. The uranium oxide 
employed was placed in a square shallow hole cut in a lead plate placed on the plate 
B. The current between A and B was determined for a potential difference of 310 
volts, an amount sufficient to practically remove all the ions before recombination. 
Fig. 7. 
Since the area of the uranium surface is small conpiared vbtli the area of the 2 )lates 
between which the uranium was placed, the total energy }ier second emitted liy the 
surface S of uranium is approximately equal to IS, where I is the intensity of the 
radiation at the surface of the uranium. 
If \ is the coefficient of absorption of the rays in air, and W is the energy required 
to produce an ion, the energy absorbed per second between the plates at a distance d 
apart is equal to 
IS[1 - = nW = -W, 
€ 
where n is the number of ions produced per second, i is the current, and e the charge 
on an ion. 
The total energy emitted per second is eijual to 
AY 
€(1 - 
