44 



X. Vladimír Novák: 



I measured the résistance of the plate before exposing it, then 

 exposed it, develloped, wasbed and dried, eut off the small stripes 

 on which the emulsion was daraaged by the previous électrodes and 

 develloping, and prepaired it for the following résistance measuring 

 in the samé manner as before. The résistances were allways cal- 

 culated for 1 cm 2 of the emulsion. The characteristic curve from 

 the observations-data was obtained in two shapes ; one beiûg the 

 ordinary Hurter-Drirlelďs opacity-curve constructed from the loga- 

 rithmus of the exposure and the number given by the Toepfeťs 

 wedge-photometer, the other from the logarithmus of the exposure 

 and the procentual change of the résistance of one cm 2 of the emul- 

 sion eaused by exposing and develloping it. 



The following table contains the results for three kinds of plates: 

 „Lumière", „Queen" and „Helsner". 



2. Table. 



Exposure 



Procentual change 

 of the résistance 



Relative opacity *) 



seconds 



Lumière 



Queen 



Helsner 



Lumière 



Queen 



Helsner 



1 



2 

 4 

 8 



12 

 \6 

 32 

 64 



— 10-5 



— ío-i 



+ 3-3 



— 15-8 



— 18-0 



— 15-9 



— 6-2 



— 1-3 



— 37 



— 9-2 



— 17-3 

 - 13-4 

 f 8-6 



— 8-3 



— 19-5 



— 92 



— 82-7 



— 86-0 



— 65-9 ! 



— 74-0 

 -71-6 



— 71-7 



223 

 27-8 

 36-3 

 41-0 

 42-3 

 43-1 

 39-8 

 37-2 



25-1 

 25-7 

 381 

 41-3 

 41-8 

 41-6 

 42-1 

 41-8 



25-2 

 27-6 

 37-6 

 41-3 

 42-4 

 411 



The new characteristic curves show a very interrestiog form. 

 The part of the curve corresponding to the normal exposure is li- 

 mited by two minimums, the maximum between them being the most 

 suitable exposure. Comparing these exposures we may get the rela- 

 tive sensitiveness of différent plates. 



mula D 



) This ralative opacity is proportional to the opacity given by the for- 



