﻿304 Mr. H. G. J. Moseley and Dr. W, Makower on 



Fig. 2 shows the theoretical curves for a recoil lasting 90 

 seconds. Curve C represents the case in which all the 



Fig. 2. 



t 40 



— — ~ ^m e — i n g 



-^-^ — I 



4- 8 12 16 20 24 28 32 



MtNu res 



Ei.«e of activity from EaB. Recoil 90 seconds. 



radiation is due to radium C ; in curve D the ratio of the 

 ionizations by an atom of radium B and of radium C is 

 taken as 6 : 100. The points marked by circles were obtained 

 through 2*95 mm. of lead in addition to the glass and the 

 walls of the electroscope. The points marked with crosses 

 were taken through the same screens as used in obtaining 

 the points on curve A, fig. 1. These results show that 

 radium B emits rays which are capable of penetrating several 

 millimetres of lead, but which are almost completely absorbed 

 by 1*5 cm. 



The experiments so far described were entirely inde- 

 pendent of each other, so that the possibility remained that 

 the differences in the curves were accidental and due to 

 contamination with radium of the surface upon which the 

 radium B was collected. In order to make sure that this 

 explanation was incorrect, an experiment was made in which 

 the same active plate produced ionization in the electroscope 

 alternately through the electroscope walls and through an 

 extra 1*2 cm. of lead. The curves so obtained were in 

 substantial agreement with those given in fig. 1, showing that 

 the initial ionization was really due to radium B. 



In order to extend the investigation to smaller thicknesses 

 of lead, a new electroscope had to be constructed. For this 

 purpose an electroscope of dimensions 20 cm. cube was made 

 with 5 sides of lead 1 mm. thick, the sixth side being closed 



