174 McCieLtanp— On Secondary Radiation. 
of the radium, and the ionisation measured at each stage. We thus get from one 
experiment the intensity of the primary rays after they have passed through 
various thicknesses of foil ; and from the other experiment we get a measure of the 
secondary rays produced by the primary after passing through the same thickness 
of foil as before. 
et 
INTENSITY OF RADIATION 
The results are as follows, the primary and secondary radiation being 
expressed so as to have a maximum of 100 in each case :— 
Sheets of Foil. Primary Radiation. Secondary Radiation 
0 , 3 : 100 : ‘ : 100 
1 : : : 61 ‘ 6 : 56 
2 : : 5 ATS : 4] 
1 : : : 40 : ; 3d1 
8 33 j : 19 
16 : 5 : 20°5 6 : 10 
32 : : : 23 6 ; : a 
The curves in fig. 3 are plotted from the above numbers. The curves show, ata 
glance, the relative efficiency of the various parts of the primary pencil in pro- 
