65(3 Mr. E. D. Kleeman on Different Kinds of y Rays 
remaining radiation. If only part of the radiation of Group I. 
is absorbed, as is actually the case, the ratio A/B is greater 
than this value. For it will be easily seen that if u is increased 
and A kept constant, B must decrease in order that the value 
of the right-hand side of the equation may remain the same. 
The value of B on the above assumption is therefore smaller 
than that of A. There is therefore little room for the radia- 
tion B to consist of a number of groups of rays of the same 
intensity as A, or the secondary rays from zinc to consist of 
a number of groups (of intensity A) much greater than two, 
It seems therefore that a large part of the primary and 
secondary radiation is represented in each case by the three 
groups of rays defined in this paper. 
The relative total amount of 7 radiation produced per 
unit mass in a substance, a quantity which will now be 
discussed, cannot be obtained, since each radiating substance 
absorbs to a large extent one of the groups of rays generated 
in the substance. Moreover, the proportion of 7 rays 
absorbed by the screen which is used to cut off the /3 rays, is 
not the same with each radiating substance but depends on 
the nature of the substance. But since the substances 
belonging to any one of the groups defined in this paper 
radiate the same two groups of rays, the values of the 
radiations obtained for a group of substances give the 
relative amounts of radiation of these two groups of rays 
produced perc.c.,if the proportion of this radiation absorbed 
by the radiator is the same with each. It will be seen that 
in this case the screen absorbs the same proportion of the 
radiation from each substance, and therefore does not alter 
the values of the radiations relatively. Table VI. gives the 
Table VI. 
Eadiator. 
Mass of 
radiator. 
Radiation 
from 
radiator. 
Radiation 
per 
unit mass. 
1 
Pb 
1652 gins. 
53-8 
527 
Zn 
1622 gms. 
100 
100 
Cu 
1890 „ 
121 
1037 
Fe 
1818 „ 
117 
104-3 
S 
1305 „ 
99-3 
123-3 
Al 
1455 „ 
105-7 
117-6 
C 
2076 gms. 
153 
119-4 
