﻿300 Drs. K. Fajans and W. Makower on the 



results are shown graphically by plotting the logarithm of 

 the activities as ordinates against the thickness of the 

 absorbing layers as abscissae. It will be noticed that the 

 point for mm. of aluminium is much too low, no doubt on 

 account of the smallness of the ionization due to RaB 

 compared with that due to RaC in these circumstances. 

 In this case the corrections to be introduced in calculating 

 the ionization due to RaB alone are so great that accurate 

 determinations become impossible. On this account all the 

 values in the fourth column of Table I. are referred to the 

 ionization produced through 0'0140 mm. of aluminium, which 

 is taken as 100 instead of referring to thickness mm. 



If we consider the relative ionizations of RaB and RaC in 

 equilibrium when measured without any screen we see that 

 the amount contributed by RaB lies between 1 and 2 per 

 cent, of that due to RaC. Now since under these conditions 

 the ionization produced by RaC is mostly due to a rays, 

 whereas that produced by the RaB is due to /3 rays, the 

 relative contributions of the two products to the total 

 ionization is about that to be expected. It will be seen that 

 as the thickness of the absorbing filter is increased the 

 proportion of the total ionization due to RaB increases to 

 the value 1"33 for a thickness of 0'044 mm. of aluminium, 

 which just suffices to cut out all the a. radiation ; it then 

 falls off again as the absorbing layer increases on account of 

 the great absorption suffered by the ft rays from RaB 

 compared with that suffered by the RaC rays. After adding 

 about *7 mm. aluminium to cut out all the soft rays from 

 RaB, the ratio of the ionization produced by RaB to that 

 produced by RaC attains the constant value 0*045, showing 

 that the remaining rays from RaB have about the same 

 coefficient of absorption as the hard rays from RaC. It thus 

 appears that whereas the greater part of the /5 radiation 

 from RaB is soft, there is a small quantity of hard radiation 

 which will be seen from the fourth column of Table I. to 

 amount to rather more than 1 per cent, of the total radiation 

 from RaB. The coefficient of absorption of these hard rays 

 is the same as that of the hard rays from RaC, which is 

 13 cm. -1 . The coefficient of absorption of the soft rays will 

 be seen from figure 4 to be 91 cm." 1 , a value which is greater 

 than the values 80 cm. -1 found by Schmidt and 75 cm. -1 

 found by Kovarik. Thus the absorption coefficient obtained 

 by us does not agree very closely with those previously 

 obtained, and the difference is no doubt in part due to the 

 fact that the experimental arrangement was somewhat 

 different from those employed by Schmidt or Kovarik ; but 



