104 



ROYAL SOCIETY OF CANADA 



and the radium. The difference between the ionization before and after 

 the radium was placed in position was recorded as due to the primary 

 rays from the radium together with the secondary rays excited by them 

 in the receiver. From Table XII it will be seen that " n/' the value 

 of the ionization in each receiver due to the presence of tûie radium, 

 varied inversely as the square of the distance " d " from the cylinder, 

 the same variation being shown graphically in Fig. 8. In this connec- 

 tion it may be noted, however, that for distances less than three metres 

 a much larger value for " n " was obtained than was demanded by the 

 law of tJie inverse square. 



TABLE XII. 



This variation from the law appeared at first sight somewhat 

 difficult of explanation. On consideration, however, of the results ob- 

 tained in the previous section, it at once seemed evident that the varia- 

 tion of " n " from the value of it demanded by the law of the inverse 

 square was but another manifestation of the same secondary radiation 

 excited by the presence of the radium in the neighbourhood of the 

 brick wall against which the electrometer was set up. 



In Table XII the value of the constant "nd^ " has been calculated, 

 giving for the receivers of Pb., Zn. and Al. respectively the numbers 

 6976, 5711, and 4996, which are thus a measure of the ionization in 

 the different cylinders due to the Y ^^ys from radium plus the second- 

 ary rays induced by them in the enclosing metals. These numbers we 

 see are in the ratio of 1.4 to 1.14 to 1.0 for the three metals Pb., Zn., 

 and Al., whereas the ratios arrived at from the figures of Table XI 



