as Photographic Agents. 261 



I turned my attention to the effects produced by the light which 

 had permeated coloured media, the absorptive powers of which 

 were carefully analysed. 



The media I was induced to adopt transmitted rays in the 

 following order. 



Blue. Ammonia-Sulphate of Copper. — The whole of the 

 most refrangible rays, from the edge of the green to the ex- 

 tremity of the violet. 



Green. Nitro-muriate of Copper. — Those rays which have 

 place between the extreme upper edge of the blue, and a line 

 which would accurately divide the pure yellow. 



Yellow. Bi-chromate of Polassa. — That portion of the 

 spectrum which would lie between a line drawn below the 

 orange, rather within the red ray, and through the lower edge 

 of the pure green ray. 



Red. A strong Solution of Carmine in Ammonia. — A por- 

 tion of the orange and all the rays below it. 



42. The most remarkable effects were produced upon the 

 papers <z, b, c, d 9 and n (13). They have been subjected to 

 similar influences, prepared with all the hydriodates I have 

 mentioned (20 — 27); but I do not feel myself warranted in 

 occupying your pages with any statement of the results on 

 any, but those prepared with the pure hydriodate of iron and 

 the hydriodate of baryta. These drawings were all well 

 washed with hot water, and when quite dry, arranged under 

 the different fluids, and exposed in a window which faces the 

 south. I will name the papers from the salt used, and the 

 colour shall indicate the rays. 



43. Hydriodate of Iron, Muriate of Ammonia. — Blue. The 

 picture nearly destroyed by the browning of the yellow lights, 

 at the same time as the darker parts have much faded. 



Green. The dark parts nearly all faded out ; the few re- 

 maining spots much reddened, but no change in the yellow of 

 the light parts. 



Yellow. Looking through the paper, the lights appear 

 darkened by a blueish-green tinge ; the dark parts, originally 

 a red brown, are changed to a blue-black. 



Red. The lights yellower than before ; the darks a deep 

 black. 



44. Chloride of Sodium. — Blue. The lights darkened, and 

 the dark parts faded and reddened. Green. Picture entirely 

 obliterated; the yellow unchanged. Yellow. The lights 

 tinged a decided blue ; shadows darkened. 



Red. The lights of a green tinge; but I consider this to 

 arise from the deepening of the yellow hue ; the dark parts 

 blackened. 



