IQ Art. 10. — S. Kinoshita and H. Ikeiiti : 



(a). Having proved that each halicle grain is rendered capa- 

 ble ()f development whenever it is encountered by an a particle, 

 equation (3) which can be written in the form : 



cls = c (sq—s) dn, (3') 



may be interpreted as: the rate at which the number of acted or 

 developable halide grains increases with the falling a particles is 

 proportional to the number of halide grains not yet acted upon. 

 And the proportional factor c will be the probability of one halide 

 grain being struck by an a particle, and consequently, the ratio of 

 the area of the projection of each grain to a plane perpendicular to 

 the direction of motion of the « particles to a unit area. 



Therefore, if Vq is the average radius of the halide grains, sup- 

 posing these to l)e spherical, 

 Tiro 



c = 



1 



from which 



H^y 



(4) 



Thus, from the values of c already given, we obtain: 



ro='Gl /^ for the Instantaneous Plate, and 

 ro="5-t fi for the Ordinär}^ Plate. 



If each grain of silver bromide of radius ^o be completely re- 

 duced to metallic silver, its mass m and radius r would be 



4 , 108 4 / c \l 108 ,.. 



8 188 3 \ 7T I " 188 ^ 



where />„ and •> are the densities of silver bromide and metallic sil- 

 ver respectively. 



As a verification of the result, the mass M of silver contained 

 in a unit area of a plate deduced from the mass m calculated by 

 equation (5) and the number s of the silver grains per unit area, 

 viz. 



.r 4 / c \§ , 108 .„x 



