186 COLOR PHOTOGRAPHY. 



layer of the silver chloride-collodion mixture and the fine-grained 

 liquid emulsion. The diameter of the grains was in the latter case 

 determined by the microscope to be about 0.001 mm. 



Regular stationary light waves are impossible in such grains. The 

 motion of light among them must be very irregular. This is the case 

 also in a still higher degree with the Poitevin films on j>aper. The fact 

 that they reproduce colors much better determined me to subject them 

 also to the prism experiment. 



It was found undesirable to have the benzene soak through the 

 whole paper, because the colors were thus made less distinct in air. 

 The spectrum reproduction was therefore cut in half perpendicularly 

 to the reference mark after drawing the latter in the yellow. One of 

 the parts was placed upon the side of an auxiliary prism II (Fig. 3 

 shows section of the prisms and leaf), and this was fastened to a level 

 glass plate, upon which the other half of the leaf was so placed that 

 the marks came together. Finally prism I, with the high refractive 

 index, was set upon the second half, benzene poured between, and the 

 eye placed in line with the reference mark and with the surface of 

 the principal prism. It was noticed that the colors under the prism 



\ 



Fig. 3. 



were a little less bright and the green and blue a little less distinct 

 This was due to the yellow coloring of the flint-glass prism, for a line 

 drawn on paper with a blue pencil appeared of a greenish tone through 

 the prism. A displacement of colors could not, however, be observed 

 through the prism. 



The sensitive substance in Seebeck's process is the same as in Bec- 

 querel's. In Poitevin's method other constituents are used, which 

 probably only lower the index of refraction of the layer. The absence 

 of color displacement shows that the colors of Seebeck and Poitevin 

 pictures are, in distinction from those of Becquerel, not interference but 

 body colors. 



X. — Seebeck's and Poitevtns' Color Pictures Observed in 

 Transmitted Light. — Second Proof of their Character as 

 Body Colors. 



The films prepared from collodion emulsion of chloride of silver 

 according to Poitevin's process show colors after exposure to the spec- 

 trum illumination when observed from behind, both in reflected and 

 transmitted light. These colors correspond in position with those 



