679 



2.0 



1.6 



1.2 



0.8 



0.4 



Silver. 

 Fig. 6. 



32 



64 



the quantity of silver per unit surface. Tlie foi'imilae used for tlie 



calculation of tlie figures on the 5"' column were 



Di — 0.1708 + 0.4138 % (2)Q Q and i)ij= 0.5473 + 0.3915 /o;/,.2) Q. 



The second formula was calculated from 3 figures only. 



For the last column I used the forinulae : 

 100 A(n = 7.055 + 12.485 %(2)Q and 100^9/f=9.74 + 6.08Zo<7(2)Q 



We see immediately from the table, that the conclusion as lo 

 the difference in the amount of silver contained in the film after 

 exposure to light and to X-rays seems to be true. We find that 

 ii and /?3 show only a slight difference in density viz. 0.663 and 

 0.622, the Röntgennegative being the more transparent one. Yet 

 this contains 0.279 mgr. of silver per unit whereas the denser light 

 negative contains onlj- 0,201 mgr. The same thing is found for 

 L.^ and R^. 



If two negatives with nearlj^ the same cjuantity of silver be com- 

 pared, for instance L^ and II.,. containing 0,201 and 0,216 mgr. 

 of silver, we find the light-negative about 50 percent denser than 

 the Röntgennegative, which, however, contains more silver. 



I must advance still another argument in favour of my theoretical 

 deductions. If these be true we ought also to expect differences in 

 the slope of the characteristic curves Avhen ordinary light waves of 

 different length are used, the absorption-coefficients of which in 

 bromide-silver-gelatine is different. In Edkr's Handbook of Photo- 



44 



Proceedings Royal Acad. Amsterdam. Vol. XVIII. 



