

556 Mr. C. G. Barkla on Energy of 
Wilson with those of Rutherford and McClung, J.J. Thomson* 
concluded that about 25 of the energy of the raysis expended 
in the ionization of the gas, the rest being converted into 
heat. We see, however, that a large fraction—for moderately 
absorbable rays of the order _—goes in secondary radiation. 
In the case of very penetrating rays the fraction is much 
larger. 
J. J. Thomson has shown that if Réntgen radiation passes 
through a medium in which there are N ions per cubic centi- 
metre each of mass m and possessing a charge e, then the 
radiation from each ion as its motion is accelerated by the 
intense electric fields in the Réntgen pulses, produces a 
diminution in the energy of the primary radiation, the rate 
of change of intensity of the primary beam due to this 
secondary radiation alone being given by the expression 

dis on Ne. 
de) Bane 
E being the intensity of primary radiation and © the 
c 
rate of change of intensity. 
‘Now it was experimentally shown that the radiation was 
independent of the ionization in the gas from which the 
secondary radiation proceeded, bunt was proportional to the 
number of corpuscles or electrons in a given volume of the 
gas, and hence it was concluded that the corpuscles constituting 
the molecules were the sources of secondary radiation. Sub- 
stituting the values experimentally determined for lat in the 
Edz 
above equation, together with the accepted values of e and m, 
we may calculate on this theory the number of corpuscles 
per cubic centimetre of air at atmospheric pressure and 
temperature, and compare this with the number assigned by 
the electronic theory of matter. 
? 

Tne 9 Oe PANG) 2 ai gece 
m 
dh _ _4410-*NE. 
ax 
: dD ; : 
But by experiment cae ot 00024 E, 
1 AN a6) ee 224 
Considering the range of possible values of e and m, there 
Bo Oe ee 
is a close agreement between the number thus obtained and 
* 
* “Conduction of Electricity through Gases,’ p. 255. 
