680 



graphy, Part III, we find on plate II a series of characteristic 

 CLirv'es pertaining to light of dilTerent wavelength between 4100 and 

 5100. The curve for 4600 shows maximal action and also maximal 

 slope. Experiments by Eder on orthochromatic plates, the curves 

 of which are given on other plates, also prove tiie fact that stronger 

 absorption or a large value for ft concurs with stronger slope in 

 the curve. 



Another fact mentioned by Eder (I.e. p. 223) is the greater density 

 of collodion negatives as compared witii gelatine-negatives containing 

 the same amount of silver. As the former are notably thinner than 

 gelatinefilms this is equivalent to a larger absorption in the thinner 

 fdms. If, finally, the thickness of a layer containing a certain amount 

 of silver is so far reduced that the conditions, present in a silver- 

 mirror are approached, Eder finds that only 0,039 mgr. of silver per 



TABLE III. 



Number 



dS 

 dL 



dS 

 dR 



Quotient 



Hardness 



Quotient 

 calc. 



7.2 Benoist 



6.1 



4.2 



8.4 



1.250 

 1.336 

 1.483 

 1.157 



Hardness 4 



Fig. 7. 



