222 



Miss Jadwiga Szmidt on the 



the absorbing foils. In Table I. the values of /x/p in the four 

 cases are given together with the corresponding values for 

 " characteristic " X rays found by Barkla and Sadler *. 



Lo0 



Fig. 2. 



of Ionization 



% I —J 1 — -1— * 



Table I. 



atomic weight. 



Iron 55*8 



Nickel Gl-3 



Copper 63'6 



Zinc 654 



Mass absorption coefficient fi/p in aluminium for 

 y rays. X rays. 



91-3 cm." 1 Al 



58-8 



46 '8 



39-8 



88-5 cm. 1 A\ 



591 

 47-7 

 39-4 



It is seen that there is a close resemblance between the 

 radiations in the two cases. The difference in values is not 

 greater than the experimental error. 



The amount of secondary radiation, never exceeding 

 5-6 divisions a minute, varied in the different cases, but was 

 as a rule larger for the lighter radiators. In the case of 

 elements heavier than zinc — namely, silver and tin — the 

 secondary effect was too weak to be examined with the 



* Loc. cit. 



