<y-Rays of Thorium and Actinium. 



149 



ranges o£ thickness of the rays of uranium X (II. p. 729). 

 There the bodies arrange themselves one above the other in 

 order of the density of the material, the lighter substances 

 giving for equivalent thicknesses far more ionization than 

 the denser. The mean values of 100 x X/d are tabulated 

 below. 



Thorium D. 



Radium C. 



Mesothorium 2. 



Lead, 2 A i 359 



4-54 



5-63 



Lead, 2B 



3-58 



4-38 



5-55 



Class II. 2 A... 



376 



4-28 



4-41 



Class II. 2 B... 



3-48 



3-78 



3-95 



It is seen that the values for lead are very near one another 

 but the differences are quite real. For radium the value of 

 \ = 0*517 has been obtained at least six times for Disposi- 

 tion 2 A. Taking the values for radium as unity the results 

 are summarized in the following table : — 





Thorium D. 



Radium C. 



Mesothorium 2. 



Uranium X. 



f2A 

 Lead... < 



[2B 



0-79 



1-00 



1-24 



1-27 



0-82 



1-00 



1-27 



— 



(2 A 

 Class II. \ 



[2 B 



0-88 



TOO 



1-03 



— 



0-92 



100 



1-045 



— 



In Disposition 2 A, the values of X are all about 5 per cent, 

 greater than in Disposition 1. In Disposition 2 B lead still 

 absorbs normally, but both Class II. and Class III. bodies 

 now obey the density law. 



Disposition 3 was only used for copper. The following 

 values of X were obtained :— - 



Thorium D. Radium C. 



Mesothorium 2. 



Uranium X. 



X Copper 0-277 0'345 



0-357 



0-432 



or relatively 



0-80 



1-00 



1035 126 



