Chemistry and Physics. 229 



includes the effect of white light in general, then that of different 

 portions of the spectrum on the plates specified, and finally the 

 effect of sensitizing the plates with various coloring matters. As 

 sources of illumination, gas, the electric arc, and solar light were 

 employed, the two last exclusively where the spectrum was 

 needed. The special arrangement of the apparatus is described 

 in detail, and then the results obtained with each of the substances 

 under examination, for the three cases mentioned. In the cases 

 when the spectrum was employed, a series of plotted curves 

 show the variation of the electromotive force for waves of dif- 

 ferent length and particularly the point at which the maximum 

 was reached. As coloring matters, various substances were 

 employed ; thus with plates of copper oxidized, eosine, safranine, 

 erythrosine, etc., were used. These had a remarkable effect in 

 changing the position of the maximum in the spectrum. 



As an example of the results obtained the following table is 

 quoted: it gives the electromotive force (E.M.F.) developed with 

 plates of copper oxidized, the effect varying widely with the 

 degree of oxidation. 



Degree of oxidation. E.M.F. developed. 



Straw-yellow _ _ - 5 X 1 0~ 5 volt. 



First violet . _ _ _ 7 



Second " 118 



Third " .- 194 



Oxid. more advanced _. 194 



Blackish _ _ _ 7 



The author concludes that by employing the substances men- 

 tioned, actinometers highly sensitive to light can be formed, the 

 electromotive force of which, other conditions being equal, 

 depends upon the electrolyte used. The maximum of sensibility 

 in the spectrum for a given wave-length depends on the nature of 

 the sensitive layer, and is independent of the electrolyte. The 

 use of the coloring matters employed serves to increase the 

 electromotive force for radiation, but gives a maximum for a 

 certain wave-length dependent upon the choice of the material. 

 This maximum always takes place for waves of greater length 

 than those which correspond for the maximum absorption of 

 light by the same coloring matter. 



In discussing various applications of such actinometers, the 



author gives, for example, the actinic degree, defined as — -, for 



various forms of light, including gas, Drummond light, the mag- 

 nesium lamp, and the electric arc. Here e 1 is the deviation of the 

 luminous point when a Carcel lamp illuminates the actinometer, 

 and e 2 the same when the various light sources mentioned below 

 are employed. The results are as follows : 



