55 



MEASUREMENT OF X-RAYS AND RADIUM 

 of the filter, are plotted new log percentage transmissions, 



y' = log (lOo£^ 



= 2/ + 2 - log (lOO^A 

 = y -\- const. 



Thus all points on the new curve differ in position from corresponding 

 ones on the basic curve by the same amount; that is, the new curve is 



(5) 



20 



2 4 6 8 10 12 14 16 18 



Aluminum Filter MM 

 Fig. 7. — Standard aluminum absorption curves — thin tube. 



obtained from the basic curve by merely shifting the origin of coordinates 



2 - log 100 



o 



to the point x = d and y = — 



The second case deals with the converse problem . given two absorp- 

 tion curves of the same radiation, but subjected to different amounts of 

 filtration; to find the difference in thickness of the initial filters. Here we 

 are supposed to have two separate absorption curves of Fig. 4— .45 on 



