<y-Rays of Thorium and Actinium. 

 Table A. — Disposition 1. 



147 





Thorium D. 



Eadium C. 



Mesothorium 2. 



Uranium X. 



\. 



lOOA/d 



\. 



100 X/d. 



A. 



100 X/d. 



5-44 



4-23 

 4-25 

 4-15 

 4-21 

 4-24 



4-21 



A. 



0-725 



100 X/d. 

 6-36 



Is 



Lead 



0-462 



4-05 



0-500 



438 



©- 



3 



0620 



0373 

 0-355 

 0-316 

 0305 

 0-300 



0-119 



Copper 



Brass 



Iron 



Tin 



Zinc 



0-294 



0-271 



0250 



0-236 



0-233 



0-0961 



00916 



0-0886 

 0-062 



334 

 3-25 

 3-28 

 3-26 

 3-30 

 3-37 

 3-24 



3-52 

 323 



Slate ... 



Aluminium 



Glass 



Magnesia Brick... 



Sulpbur 



ParafBn Wax 



0-113 

 0090 



0-083 

 0-050 



4-48 

 4-69 



4-65 



5-80 



0-122 

 0-0917 



00921 

 00433 



4-84 

 4-78 



5-16 

 5-02 



066 

 0031 



3-69 

 3-61 



0-078 

 0-040 



4-38 

 4-64 



The nature of the absorbent has a marked effect on th 

 relative penetrating power of the four types of rays. Taking 

 the values for radium G as unity, this is shown in the 

 following table, mean values for Class II. being employed. 



1 



1 



Thorium D. 



Radium C. 



Mesothorium 2. 



Uranium X. 



Lead 



924 



100 



1-24 



1-45 





Class II 



0-82 



1-00 



1-06 



1-18 



In Disposition 2, with the absorbing plates clamped up to 

 form the base of the electroscopes, two sets of experiments 

 were performed, namely (2 A) with the preparation bare, 

 and (2 B) with the preparation covered with 0'6I cm. lead, 

 to see if the hardened rays produced would be exponentially 

 absorbed by all bodies according to the density law. The 

 result shows that this is the case except for lead. Table B 

 (p. 148) shows the results obtained. 



All absorption curves for this disposition are also expo- 

 nential after 1 cm. of equivalent thickness of lead has been 

 traversed. The curves made by plotting equivalent thickness 

 of metal against the logarithms of the ionizations are co- 

 incident. So they are also in the case of Disposition I. 

 This holds both for Dispositions 2 A and 2 B. This is 

 opposite to what was previously obtained with a brass elec- 

 troscope for the absorption by bodies over small initial 



L2 



