for Measuring Ionization. 723 



sensitiveness of the electrometer does not affect the accuracy 



of the reading. 



Table III. 

 X rays. 



1 



Absorbing- 

 Material. 



1 



Balance- 

 point. 



Relative 

 Intensity. 



Per cent. 



Unabsorbed 



Rays. 



Per cent. 



Unabsorbed 



Rays. 







1)4-0 



89 



100 



Note. — In these 



1 layer aluminium. 



61-5 



70 



79 



observations the 



2 



46-5 



58 



65 



layers were added 



3 ,',' " 



39-0 



51 



57 



successively, the 



4 ., 



36-0 



47 



52 



one for brass in- 



5 „ »> 



31-0 



42 



47 



cluding all the 



6 „ 



25-5 



33 



37 



aluminium. 



7 „ 



24-0 



30 



33 





1 „ brass. 



18-3 



17 



20 



100 



1 ,, iron. 



14-3 



7-0 



7-9 



39 



2 „ 



12-8 



4-5 



5-0 



25 



4 ,', !, 



1-1-5 



3-0 



3-3 



17 



10 „ „ 



10-5 



2-3 



2-6 



13 



Thickness of ea 



ch aluminium layer *C 



50 centim. 





55 55 



iron 



„ •< 



)58 „ 





55 >.• 



brass 



5, '( 



H8 „ 







7 faj 



r s. 











200 



22-0 



100 





1 layer iron. 



19-4 



21-0 



95 





3 .„ 



184 



17-2 



79 





6 „ 



171 



140 



64 





10 „ 



160 



11-5 



52 





20 „ „ 



14-9 



8-2 



38 





30 „ „ 



14-1 



65 



30 





In Table III. are also shown some results with the y rays 

 of 5 milligrams of pure radium bromide. A comparison of 

 the penetrating power of the two types of rays shows that 

 the softest 7 rays are about equal in penetrating power to 

 the hardest X rays the tube was capable of giviug. 



The above described instrument on account of being com- 

 pact, portably accurate, and easily manipulated, may commend 

 itself to those engaged in research in radioactivity, or other 

 form of ionization, as a standard instrument. 



University of Cincinnati, 

 June 1907. 



