146 Messrs. A. S. Russell and F. Soddy on the 



as the electroscope is not disturbed. Disposition 2 is similar 

 to that used in obtaining Table I. (I, p. 633) except that the 

 electroscope is of lead as in Disposition 1. It offers certain 

 theoretical advantages, but is more difficult to work with. 



Fig. 2. 



o 



ABSORBENT 



ABSORBENT 



/ 



TAD" 



ABSORBENT 



LEAD 



2A 



The only reason for using Disposition 3 was that uranium X 

 had once been examined with it. It was not possible to 

 prepare uranium X for the present set of measurements, but 

 many of the previous results can be utilized. Those of 

 Tables II. and III. (I. pp. 644 & 646} only differ from the 

 present Disposition 2 in that a wood stand instead of a lead 

 stand was used for the preparation, but parallel experiments 

 with mesothorium 2 showed that this had no effect on the 

 values of \. The results with Disposition 1 are tabulated 

 in Table A. 



After a thickness equivalent to 1 cm. of lead (total thick- 

 ness, with base, 2 cm. of lead) all the curves are exponential. 

 Lead is in a class by itself (Class I.) with high value for \\d 

 throughout. The Class II. bodies have an approximately 

 constant A/rf, but the limit of density down to which this 

 holds is greater for the more penetrating rays than for those 

 less penetrating. The lightest bodies (Class III.) have again 

 higher values for \jd. 



