the Absorption of the Gamma Rays. 

 Table II. — Iron. 



137 



Thickness 



Mass 



of 



Unit Area 



(P*)- 





Ionization Current. 



Apparent 

 Scattering 

 in forward 

 direction 



(S). 



of 

 Plate 



r~ 



Source 



alone. 



Plate in 

 Position 1. 



Plate in 

 Position 2. 



cm. 

 •0926 



gr.-cm.- 2 

 •727 



100-0 



98-17 



95-87 



2-30 



•195 



1-528 



„ 



96-18 



91-59 



4-59 



•287' 



2-25 



)( 



94-39 



88-53 



5-86 



•388 



304 



9J 



92-41 



85-09 



7-32 



•480 



3-77 



,, 



90-45 



82-01 



8-44 



•581 



4-56 



)) 



88-65 



78-88 



9'77 



•673 



5-28 



;> 



86-73 



76-10 



10-63 



•763 



5-99 



» 



84-75 



72-92 



11-83 







Table III. — Lead. 





Thickness 



Mass 



of 



Unit Area 



(Pi)- 





Ionization Current. 



Apparent 

 Scattering 



of 



Plate 



(t). 



r 



Source 



alone. 



) Plate in 

 Position 1. 



Plate in 

 Position 2. 



in forward 

 direction 



(S). 



cm. 

 •061 



gr.-cnv 2 

 •696 



1000 



97-30 



95-46 



1-84 



121 



1-38 



>> 



91-39 



94-38 



2-99 



•180 



2-04 



5? 



87-79 



92-13 



4-34 



•240 



2-73 



„ 



84-59 



89-74 



5-15 



■300 



3-41 



)5 



81-17 



87-31 



6-14 



•441 



5-01 



»J 



73-60 



81-65 



8-0 



•561 



6-38 



1> 



67-66 



76-33 



8-67 



•705 



8-02 



>5 



61-53 



71*25 



9-72 



•825 



9-38 



J» 



56-74 



67-01 



10-27 



The values S, given in the 6th column of the Tables, 

 entitled " apparent scattering in forward direction," are 

 simply the difference between the values given in the 5th 

 and 4th columns. The theoretical expression for S is 

 given by the formula (6) or (6'). These values of the 

 apparent scattering must be smaller than the true values, 

 since the scattered rays were reduced by absorption in 

 escaping from the radiating plate. In rig. 3 the values 

 of S are plotted against pt. It is seen that the curves are 

 not straight lines, but gradually slope towards the axis 

 of pt. This is an indication that the scattered rays are 

 reduced by absorption. The curve for lead is much lower 

 than those for aluminium and iron ; while the curves for 

 the two latter nearly coincide. This point will be discussed 

 later. 



