156 Sir E. Rutherford on the Penetrating Poiver of 



De Broglie. By plotting the logarithm of X (fig. 1) against 

 the logarithm /jl/p for lead, Hull has shown that the o curve is 

 nearly a straight line AB. At B, where a- = 0*149 A.U., the 

 absorption suddenly increases, shown by the nearly horizontal 

 line BC. Assuming that the law of absorption after passing 



Fig. 1. 



'1*4 



f-3 



1-2 



3 



2-9 



2-8 



2-7 

















•V 















s 



X. 





) 











''A 



r 





c 

















1 





y 

















< 



D 











; 



• 

















s 



X 



j 













i 



12 1*4- 1-6 1-6 00 -2 -4 -6 



Log if for Lead 

 P 



» 



through the absorption-band is similar to that observed 

 before, the line CDE should represent the new portion of the 

 curve. The circles represent values actually found by Hull 

 and Miss Rice. Taking the quantum relation, \ = 0*149 A.U. 

 corresponds to 83,000 volts, and the minimum corresponding 

 value of fi/p for lead found by Hull was 1*50, i. e. /z = 17*5. 

 From the dotted portion of the curve the radiation emitted 

 between X = 0*149 A.U. and A, = 0*098 A.U., i. e. between 

 s3,000 and 125,000 volts, should be more absorbed than that 

 emitted for voltages slightly less than 83,000. We should 

 thus expect the value of fju for the end radiation to be sensibly 

 constant for the above range of voltages. Actually we find 

 /jl nearly constant between 92,000 and 144,000 volts. This 

 difference is not important, and is to be anticipated from the 

 nature of the measurements. A radiation more penetrating 



