Elektrické měření účinku světla na desku fotografickou. 43 



sensitive electrodynamometer of Hautmann & Biu un. The plňte was 

 closed in a box situated horizontály and could be exposed to tbe 

 light of an Áuer-bnrner. The constancy of the source of light was 

 studied with a wedge-photometer. First in all it was prooved fchat 

 a plate prepared with the method above, had a constant résistance 

 at a constant température for 8 or 10 hours. 



The résistance at the température t (R t ) dépends on the tem- 

 pérature as follows 



R t -R {{ — at + ßt 2 } 



where R is the resistauce at 0°, « and ß are constants for the 

 samé sort of plates. For ušed Schleussneb's plates I found 



a — 0-0326 ß — 0-00038 



The following table contains the results of the measurement 

 on a Schleüssner's plate. 



The change of the résistance 

 absolutely procentualy 



Time 



Resistance 



of exposure 



in 100 JI 



minutes 



at 20 n C 







3638 



5 



3633 



14 



3644 



21 



3649 



25 



3670 



30 



3677 



70 



3672 



81 



3664 



99 



3627 



114 



3614 



— 5 



-0-14 



+ 6 



+ 017 



11 



0-30 



32 



0-88 



39 



1-08 



34 



0-93 



26 



0-71 



— 11 



- 0-30 



— 24 



— 66 



The changes of résistance being the effect of the light on the 

 plate were as it could be expected very sinali, the maximal change 

 reaching about 1'3%- Neverthelles the curves constructed from the 

 observation-data showed that there is a little diminishing of the ré- 

 sistance at the beginning of the exposure, afterwards the résistance 

 inereases with the inereasing exposure to a maximum. If the expo- 

 sures were stopped and the résistance of the plate measured in 

 darkness for some time, they were observed changes, which could be 

 clearly explained with the photographie induction. 



II. The resistance-method was employed also with the devello- 

 ped plates, in order to show the con-ent between the electric and 

 Photometrie method, 



