THE BEGINNINGS OF PHOTOGRAPHY. 355 



Thus the whoh> })ri>smatic .spectrum acquires a new dignit}' as chem- 

 ical. In whit(> light, both forces, oxidation and the characteristic 

 deoxidation, are in a state of opposite combination. The whole spec- 

 trum is divided into two parts, the sphere of the one toward the 

 red being- oxidation, and of the other, toward the blue, deoxidation. 



In a third experiment a long, darkened strip of the chloride paper was 

 placed in the spectrum for tive or ten minutes, when the outer ends of 

 the strip were found unchanged; but the whole blue and violet side had 

 darkened, the maximum being beyond the visible violet ra3^s, as in the 

 first experiment. The whole of the red end, on the contrary, became 

 lighter, and the maximum bleaching action was, as before, beyond the 

 visible red rays. Similar results were obtained by exposing a strip of 

 the white chloride paper in aliright light and at the same time throw- 

 ing the spectrum upon it. 



After discussing the relative oxidizing and deoxidizing powers of the 

 two ends of the spectrum and expressing his desire for exact measure- 

 ments of the intensity of the energy of the various rays throughout 

 the spectrum, as well as of its extent, he says that in chemistry it is 

 known that Avator is the chemical medium in all j^rocesses of oxidation 

 and deoxidation ])v the wet method. By it alone can the oxidizable be 

 oxidized and the oxidized deoxidized, and in both cases decomposition 

 of the water takes place. In the first case the oxygen combines with 

 the oxidizable body and the hydrogen is set free or combines with an}" 

 oxygen present in a free or combined state to form water anew. In 

 the second case tlie hydrogen of the water combines with the oxygen 

 of the oxidizal)le ])ody to form water, while the oxygen formerh' com- 

 bined with the hvdrogen of the water goes to the oxidizable body 

 present, the deoxidation of which it usually only indirectly brings 

 about. The active agent in the hrst is therefore oxygen, and in the 

 second is something which possesses the same strong affinity for 

 oxygen as hydrogen, or is hydrogen itself. He gives as a parallel 

 the decomposition of water by electricity or magnetism. In a later 

 paper he completes the parallel by showing that if the two poles of a 

 voltaic pile are placed in half -blackened silver oxide or chloride the 

 negative polo increases the darkening, while the positive entireh' pre- 

 vents it. Perfecth' dry horn sih'er appears to remain perfectly 

 unchanged in sunlight in consequence of the want of water to be 

 decomposed and supply the hydrogen necessary for the reduction. In 

 this theory of the action of water he (juite supports the theory put 

 forward ])y Mrs. Fulhame. The fact that perfectly dry silver chloride 

 exposed in a vacuum remains white has ))een proved by Sir VV^illiam 

 Abney. 



Although it appeai-s from a later paper that Ritter saw how impor- 

 tant his results would l)e in connection with the action of light on 

 organic bodies, it is curious that he made no similar experiments with 



