46  McCretuanp anp Hackerr—The Absorption of B Radium Rays by Matter. 
Resutts oF EXPERIMENTS. 
It would occupy too much space if we gave details of all the observations. 
We give the numbers in some detail in the case of one of the substances 
examined, and the collected results are shown in a table. 
Observations are first taken with no covering at P (fig. 1.), so as to obtain 
the intensity of the incident rays. Although not shown in the figure, the 
opening in the lead screen is so formed as to make the issuing pencil of 
B rays as cylindrical as possible, and to avoid strong secondary radiation from 
the lead near the place of emission. But even with such an opening there 
is some radiation in directions corresponding to large values of 6. Of course 
the radiation in these directions is of much greater relative value when a plate 
of the substance under examination is placed over the opening at P. 
With no covering the radiation for different values of # is given in the 
following table in the column headed A, and the other column gives the 
product of R and the corresponding value of sin@. The actual observations 
are reduced to the standard of 1000 for 6=0. It should be mentioned that 
all through the paper the small effect produced by y rays is corrected, so 
that 8 rays only are considered :— 
0. R. R sin 0. 
0 | 1000 = 
SO | g0B 78:7 
102 | 800 139°0 
15° 501 129°6 
20° 314 107-4 
30° 111 555 | 
45° 23 16°3 
60° 7 6-06 
75° == = 
Curve 1 in fig. 2. is plotted from the values of Asin #, and the area 
enclosed is found to be 140°5 on the scale employed throughout. This relative 
value 140°5 for the energy of the incident radiation is used throughout, care 
being taken to reduce all observations to the same standard. 
A plate of zine, of known thickness :00786 cms., is now placed over the 
opening at P, and a similar set of observations taken ; and also with a thicker 
