different Metals by Eontgen Rays. 



289 



aluminium leaf about *001 mm thick. Curves were then plotted, 

 having for abscissae the thickness of aluminium in millimeters, 

 and for ordinates the ratios of intensity of ionization after 

 absorption to the intensity before absorption. 



Since the penetrating power of the secondary rays depends 

 upon that of the primary rays, it was necessary to keep the 

 Eontgen ray tube very constant, and to have some standard of the 

 penetrating power of the primary rays. A self-adjusting tube 

 was used which was found to be fairly constant. The stand- 

 ard of penetrating power or hardness of the primary rays was 

 arbitrarily taken as the ratio of the ionization produced by the 

 rays after passing through a sheet of aluminium - 82 mm thick to 

 that produced by the unobstructed rays. This ionization was 

 measured in the chamber, " A," after connecting the chamber, 

 " B," to earth, and entirely closing the opening, "WV The 

 hardness of the primary rays was varied by varying the length 

 of the spark gap in the regulator, and by filtering out the soft 

 rays by a thin iron screen. 



Absorption curves were plotted for the secondary rays from 

 lead, zinc, nickel, copper, tin, and silver for two different de- 

 grees of hardness of the primary rays. In the case of lead four 

 curves were plotted for four different hardnesses of the primary 

 rays. The curves are represented by the full lines passing 

 through the circles and crosses. In every case the circles rep- 

 resent rays produced by soft, and the crosses rays by hard, 

 primary rays. The following tables give the data from which 

 the curves were plotted. Tables 1 and 2 refer to lead, 3 to zinc, 

 4 to copper, 5 to nickel, 6 to tin, and 7 to silver. 









Table I. 









r~ 



Hardness=0"62 — 



V 



, 



-Hardness = 



=0-89 ; , 



I 



II 



III 



IV 



II' 



III' 



IV 







TOO 



1-00 







1-00 



1-00 







•001 



0-29 



0-22 



—0-66 



0-49 



0-45 



—0-35 



•002 



0-15 



0-07 



—1-15 



0-24 



0-19 



—0-72 



•003 



o-io 



0-02 



— 1-70 



0-11 



O'Oti 



—1-22 



•004 



009 



o-oi 



—2-00 



0-08 



0-03 



—1-52 



•008 



0-07 





Table II. 



0-03 



-- 







1 Hfl.rd.D Qco — n*Ai 







-Hardness= 

 III' 



=0-95 , 



IV 



I 



ii 



III 



IV 



II' 







1-00 



1-00 







TOO 



1-00 







•001 



0-32 



0-24 



—0-62 



0-44 



0-40 



—0.40 



002 



0-19 



o-ii 



—0-96 



0-25 



0-21 



—0-68 



'003 



0-12 



0-03 



— 1-52 



0-12 



0-11 



—0-96 



•004 



o-io 



0-02 



—1-70 



0-09 



0-04 



—1-40 



•008 



0-07 







0-02 





.. 



