PHYSICAL MEASUREMENT OF X-RAYS. — BRONSON. 27 



N = total number of ions per c.c. produced in the testing 



vessel during time t. 

 e = charge on an ion — 4.7X10~~^° E. S. units. 

 /: = galvanometer constant — 3.0X10~'° amperes per mm. 



deflection. 

 d = deflection of galvanometer. 



5 = charge passing through the galvanometer in time i. 

 Then q = NeV E. S. units (if there is no recombination). 



also q = kdt coulombs 



and ^eY={kdt) 3X10^ 



In the experiments with the photographic plates, as 

 has been stated, t was so chosen that di = 200, and V was 

 100 X 4.5 = 450c.c. 



. 3X10-^°X200X3X10 9_ 



' • •^- 450X4.7X10-^° -8.5X10 



Of course the value of N necessary to produce a satis- 

 factory radiograph depends on the plate used and upon the 

 method and time of development. 



T. J f 



The average value of the constant K = — — found in the 



V 



experiments with the Sabouraud pastille was 2.5X10~^. 



As above 



k dt ZXIO^ 



N = - 



Ve 



9 f; N/ 1 n— 8 V 5 \^ 1 09 



= 1.6X10^^ 



4.7X10-^0 



This, then, gives the number of ions per c.c. formed in 

 the air immediately surrounding the pastille during a change 

 in tint corresponding to one number on Hampson's radio- 

 meter. Now the normal or epilation dose is determined by 

 tint B, as it is called, and corresponds to a change equivalent 

 to four numbers. Therefore, the number of ions per c.c. 



