McCieLiand and Hackrtrr—The Absorption of B Radium Rays by Matter. 47 
plate of -0159 ems. he following table gives the observations on same scale 
as before :— 
| Zine. °00786 cms. thick. Zine. -0159 cms. thick. 
e R. R sin 6. R. R sin @. 
0° 204 ie | a6 at 
15° 150 38:9 | 837 21:7 
30° 85 42°5 | 68 315 
ra 5chnte|n48 34:0 | 32-2 29:8 
60° 23 19°8 Weuntle:6 14-4 
75° - 8-6 8:3 8:3 8-0 
Curves 2 and 3 in fig. 2 are plotted from the values of R sin, and the areas 
enclosed are found to be 89 and 60 respectively. 
INTE ae 
Cer se 
1 aan | im EAs 
EEN al 
cic 
Wl IS 
wed =i eS ae 
Ve it a oe 
DEGREES 
Fig. 2. 
Rx sin O 
ee 
ia 
For an incident radiation of 140°5 we have, therefore, a transmission of 89 in 
the case of the thin zine plate, and of 60 in the case of the thicker zinc. When 
