PHYSICAL MEASUREMENT OF X-RAYS. — BRONSON 



25 



through the testing vessel is changed by various thicknesses 



of lead or aluminum placed over the opening F, and in each 



case the hardness was measured by a Benoist penetrometer. 



Table II shows the nature of the results obtained in a single 



experiment. 



Table II. 



Hardness. 



Sheets of Lead Foil, 

 each .26inm thick. 



Gal. Defl. 



% of Max. Defl. 



9 Benoist 



100 

 47 

 29 

 14 



Table III gives a summary of the results obtained with 

 different tubes of various degrees of hardness. Columns 3 

 and 4 give the thickness of lead and aluminum necessary to 

 reduce the ionization to half value. Column 5 gives the 

 ratio of the ionization when there are two and when there is 

 only one sheet of lead foil over F, and column 6 gives a 

 .similar ratio of the ionization for 4mm and 2mm of aluminum. 



Table III. 



Tube. 



Hard.iess. 



3 



4 



5 



6 



No. 



1 



9 Benoist 



.036mm 



4.4mm 



62% 



73% 



No. 



2 



7 Benoist 





3.5mm 





64% 



No. 



2 



6 Benoist 



.023mm 





45% 





No. 



2 



5 Benoist 



.018mm 



1.7mm 



28% 



43% 



No. 



4 



7 or 8 Benoist 



.030mm 



3.6mm 



55% 



68% 



In practice it would be much easier and quicker to 

 obtain the hardness of a tube from the data of column 5 

 or 6 than from 3 or 4. It is a well known fact, which is alo 

 clearly shown in Table III, that X-rays become less and 



