X2 Art. 10. — S. Kincshita and H. Ikeuti : 



C3^1inder drawn round the path of the a particle with radius equal 

 to that of halide grains. Consequently, .Si, which is the reciprocal 

 of the average distance d between successive grains along the 

 track, will be the number of the halide grains having their centres 



Q 



within the cylinder of unit length; thus — V will l)e the total 



number of the halide grains initiall}^ present in the emulsion film 

 23er unit volume. 



If t is the thickness of the film, the total numl)ar ,So of the 

 halide grains in a unit area of the plate will be 

 sd 

 Tin 

 Another relation l)etween ,^o and )\ can be obtained from a 

 consideration on tlie amount J/o of silver bromide contained in a 

 unit area of the plate, 



■M"o=— -- ro ,Oo Su» 

 o 



where /r>o is, as before, the density of silver bromide. 



From the above two equations, we obtain 



3 lU 



From a set of measurements made on an Ilford Process Plate, 

 e.g. 



Sj=3,500 per cm., 



-^0=9*6. lO^^gr. per sq. cm., which was determined by chemical 

 analysis, and 



^=15 J«, which was measured by Zeiss' s Dickenmesser, 

 the average radius of the halide grain is found to be 



By using the relation in equation (0), tlie average radius of 

 the silver grains becomes 



V 188 /> / ' 



A suitable photometer ])eing at present not at our disposal, 

 we are unable to compare this result witli that deduced from the 

 photometric density. It may only be noted that the above 



