Secondary y Radiation. 433 



to the leak produced by the natural ionization in the chamber, 

 to the radiation which comes directly from the Ra and has 

 not all been cut off by the interposed screens, such as L, L, 

 and to secondary y radiation from surrounding bodies, which 



Fte. 7. 



To Earth 



Y^m^ vm"rw?mm<i^ 



EMga pa^ 



20cms. 



The radiators shown by horizontal dotted lines below j>, p intercept the 

 radiation from the Ra. By means of Pb plates L, L an amount of 

 the secondary radiation may be prevented from entering- the ioniza- 

 tion-chamber. The dotted conical chamber was used in a separate 

 set of experiments. 



may bo able to enter the chamber. This latter quantity was 

 found to be by no means negligible, and so far as I know 

 has not been allowed for in many experiments by previous 



