136 Messrs. A, S. Russell and F. Soddy on the 



different positions are readily obtainable. The final results 

 are given in the following table, in terms of the ratio for 

 radium C which is taken in each position as unity. 



Positions : 





ft- 



ft. 



ft- 



ft. 



0800 



ft- 



y 1 /j3 Mesotborium 2 ... 



1-036 



0-935 



0-676 



0-524 



y,/j3 Thorium D 



0-690 



0-637 



0-568 



0-510 



0336 





For actinium the 7-rays were m ensured also through 

 0*95 cm. zinc (74) as well as through 0*3 cm. lead (7,). This 

 was done because, as was shown previously by Godlewski 

 and confirmed later in this paper, the 7-rays of actinium are 

 abnormally highly absorbed by lead. Radium C, the ratio 

 for which is again taken throughout as unity, was also 

 measured under the same conditions for comparison. The 

 final results are: — 



Positions : 



! ft. ft. 



ft- 



ft- 



ft- 



7i//3 Actinium C 



0077 ! 0-005 



0-072 



065 



067 



7 4 //3 Actinium C. 



0128 | 0-103 



0-116 



0105 



0-109 





It will be seen that the general effect of decreasing the 

 distance of the preparation in the /3-ray measurements is to 

 decrease the y/j3 ratio, to about one half, over the range of 

 distance examined, for mesothorinm 2 and thorium D ; but 

 for actinium C the difference is less marked. ]So doubt the 

 causes of this are very complex. In the first place it is to 

 be expected that the scattering of the /3-rays by the air 

 between the preparation and the electroscope will be the 

 greater the less penetrating the /3-rays, which, in descending 

 order of penetrating power, are-— radium C, thorium D, meso- 

 thorium 2, actinium C. Then, with diminishing distance and 

 greater angle of the cone of rays entering the electroscope, 

 the effect of u reflexion " of the rays from the inner sides 



