
Secondary Réntgen Radiation. 5dd 
air and of cross section 25 sq. em. giving rise to this secondary 
radiation 
194 
= _ = 7 Sem, 
25 

Hence the energy of secondary radiation proceeding from 
1 em. length of the primary beam ere through air at 
atmospheric pressure and about 15° 
00000816 x 230 
7°8 
= 00024 of energy of primary radiation 
passing through. 

We thus see that the energy lost by secondary radiation is 
a considerable fraction of the total absorption, which is of the 
order -W01 of the energy of the primary beam per centimetre. 
As this radiation is most intense in the direction of pro- 
pagation of the primary radiation, the primary beam is 
aeefarced by a portion of the Reenuidar y so that the total loss 
of intensity of a beam whose breadth is not small in comparison 
with its length i is not so much as indicated above. 
It was shown in the previous paper that the energy of 
secondary radiation is proportional to the density of the gas 
through ‘which the primary beam passes. W hen we take 
into Geta derabion the loss of energy due to this secondary 
radiation, a considerable fraction of the absorption coefficients 
is accounted for and the ratio of ionization produced to 
absorption proper (neglecting the absorption due to secondary 
radiation) is mere nearly a constant than the values given by 
Rutherford show. I think that the variations from this were 
all within the limits of experimental error *. 
The close agreement between the ratio of absorptions found 
by Rutherford and the ionizations found by J. J. Thomson f 
for carbonic acid gas and air is accounted for by the fact 
that for the gases named, the ionizations for a given radiation 
are proportional to the densities of the gases. But the energy 
of secondary radiation is also proportional to the density “OE 
the gas, hence the sums of the energies lost in ionization ‘and 
by secondary radiation are in the same ratio. 
We thus find that the energy of Réntgen radiation lost by 
secondary radiation from gases at atmospheric pressure and 
temperature is very large compared with the energy lost in 
the work of ionization. 
From the results of experiments of Townsend and H. A. 
* vhil. Mag. [5] xliii. p. 241 (1897). 
1 Conduction of Electricity through Gases,’ p. 251, 
