22 PHYSICAL MEASUREMENT OF X-RAYS. — BRONSON. 



time of exposure and the deflection of the galvanometer 

 was always 200. 



The procedure in a particular case where six sheets of 

 lead foil, each .026mm. in thickness, was to be the subject 

 radiographed, was as follows: The six sheets of foil were 

 first placed over the opening F, the tube was started up and 

 the galvanometer deflection was 30mm. The foil was then 

 removed from F and a small photographic plate was placed 

 at C. Upon this there were placed, side by side, three 

 strips of lead containing respectively 4, 6 and 8 thicknessess 

 of the above foil. The strips with 4 and 8 thicknesses each 

 were used merely to have some contrast on the negative. 

 The plate was then exposed for -30-= 7 sec, with the tube 

 working under as nearly as possible the same conditions 

 as previously. 



Over one hundred radiographs were taken as described. 

 Various thicknesses of glass, aluminum and lead were used 

 as the subjects for the radiographs and the rays in the different 

 experiments differed widely in their characteristics, but the 

 negatives showed practically the same photographic action 

 on those portions covered by the materials under examina- 

 tion. Table I gives a record of six plates, all having lead 

 foil for the subjectjof the radiograph, but taken with rays 

 which were very different for the different plates. The 

 first three were taken with a 17cm. tube having a tungsten 

 target and using an interrupterless current and the last 

 three with a 13cm. tube having a platinum target and operated 

 by a small induction coil and a mechanical interrupter. 

 The density of the negatives appeared to be alike within 

 the limits of accuracy of the various measurements.. 



