22 JBumstead — Heating Effects produced by Rontgen Mays. 



to account in this way for the observed difference in the heat- 

 ing of the lead and the zinc, we must assume that at least half 

 of the energy of the primary rays absorbed in the zinc escapes 

 in the form of secondary rays ; this is on the supposition that 

 none so escapes from the lead ; if the lead loses any energy in 

 this manner then the fraction for the zinc must be greater than 

 one-half. It appears therefore that the experimental results 

 cannot be accounted for in this way. 



Numerical Results. 



The measurements of the absorptions of lead and zinc ran 

 so nearly parallel throughout the course of the experiments, 

 with rays differing considerably in penetration, that it was 

 eventually considered unnecessary to make a separate correction 

 to each measurement with the radiometer. The absorptions 

 were measured from time to time during the investigation and 

 the results are given in the following table ; the numbers give 

 the fractions of the primary rays absorbed by aluminium of 

 the same thickness as the window, and by lead and zinc of the 

 same thickness as the strips, the latter being behind the alumi- 

 nium except in the first three experiments when no aluminium 

 was interposed. The last experiment in the table is the one 

 made with the radiometer instead of the electroscope. 







Absorptions, 





Pb 



Zn 



Exp. 



Al 



Pb 



Zn 



I 





0-925 



0-924 



1-001 



II 







0-926 



0-920 



. 1-007 



III 





0-944 



0-947 



0-997 



IV 



0-57 



0-862 



0-856 



1-007 



V 



0-45 



0-790 



0-780 



1-013 



VI 



047 



0-830 



0-803 



1-034 



VII 



0-45 



0-809 



0-805 



1-005 



VIII 



0-31 



0-684 



0-684 



1-000 



IX 



0-34 



0-676 



0-648 



1-043 



X 



0-32 



0-675 



0-655 



1-031 



XI 



--- 



0-907 

 Average 



0-880 



1-030 

 1-016 



The average value of the ratio is applied as a correction in 

 the energy measurements below. 



The energy measurements are given in the following table. 

 Column I gives the time of exposure of the strips in minutes. 

 Columns II and III give the deflections in centimeters, pro- 

 duced by exposure of the lead and zinc respectively. These are 

 the observed deflections, corrected for the effect of the induc- 

 tion coil upon the magnetic " torsion head" ; this was always 



