The electrie nieasiiremeiit of tli e effect oi' the 

 light on the photographie plate. 



By Ph. Dr. Vladimír Novák, 

 Privat-docent of the Bohemian University, Prague. 



(Pres. on 7th February 1902.) 



The only existing ínethod in studying the effect of the light 

 on the photographie plate is the Photometrie one. The method consists 

 in exposing the studied plates to a normal source of light from 

 a constant distance and in measuriug the opacity of the plates, which 

 were simultaneously and normály develloped. 



The opacity of a develloped plate (negative) is defined by means 

 of the équation 



L 



D = l0£ 



where i is the intensity of the light falling on the plate and / 

 the intensity of the transmitted light. The relativ measurements of 

 the opacity can be made with Hautmann's microphotometer using 

 a plate exposed in Scheiner's sensitometer for comparing. If this 

 plate, containing the scale of the opacity, is graduated with an ab- 

 solute photometer, the relativ measurements can be changed in ab- 

 solute. 



The correctness of the method was proved by Edee, who mea- 

 sured the mass of reduced silver in the emulsion and found the samé 

 opacity on plates, which contained the samé amount of silver on 

 one cm' 1 . According to the Bunsen-Roscoe's law the effect of the light 

 on certain plate ought to be the samé if the product of time and 

 intensity of the light ušed is constant. This law holds only in certain 

 limits, beside that the effect is smaller, when the exposure is made 



