Primary and Secondary 7 Rays. 



931 



radiation even approximately; but by integrating over the 

 distributed curves there appears to be about 20 to 30 per cent, 

 of the ionization due to the secondary radiation emitted from 

 the radiator. 



Fiff. 4. 



Position of electroscope. 



Curves showing relation between position of electroscope and the amount 

 of secondary radiation when the thickness is constant for each curve. 



A study of the curves shows that as the thickness of 

 radiator increases the point A will approach more rapidly 

 than the points on the radial lines. It is not desirable at 

 present to attempt to attach much meaning to the exact form 

 of these curves, as it is possible that the shape would vary 

 with the arrangement of the apparatus. The radium could 

 not be placed symmetrically with respect to the radiator, 

 but had to be placed against the lead screen. The gradual 

 change in volume of the radiator due to a change in thick- 

 ness from 1'05 to 11 cm. undoubtedly has a disturbing 

 influence. 



It was thought possible that these results might be affected 

 by secondary radiation from surrounding bodies, quite apart 

 from the radiator itself. To test this point and to examine 



