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ANNUAL OF SCIENTIFIC DISCOVERT. 



only over one side. The proportion of chlorine necessary for the experi- 

 ment varies in the following proportions : 



In the Memoir will be found all the indications relating to the different 

 circumstances of the preparation of the sensitive layers, circumstances 

 which should not be neglected. 



By employing a thicker layer than those above mentioned, the results 

 obtained will not be so satisfactory. We should therefore operate between 

 the limits of from 4 to 7 cubic centimeters of chlorine at the ordinary 

 pressure per square decimeter of the surface of the silver ; but in these 

 conditions, the thinner the layer, the more sensitive will the surface be, but 

 the less beautiful will be the tints obtained. 



If we project a luminous spectrum on to a sensitive surface thus pre- 

 pared, we very soon gain an impression beginning with yellow and orange, 

 that is to say, with the most luminous portions of the prismatic image, 

 and extending to the red and violet texremities. This impression, as I 

 have shown in a previous Memoir, reproduces the different shades of color 

 of the spectrum. But the shades, although very bright, are very dark ; 

 and on the red side, between the lines B and A, and beyond A, the impres- 

 sion becomes violet, and darkens rapidly. When the preparation has been 

 made according to the directions in this Memoir, no impression is repro- 

 duced beyond the violet ; and except the black color on the red side, the 

 image does not extend much beyond the limits A and //, and occupies the 

 same extent as the visible spectrum. 



If mixed luminous rays strike upon the sensitive surface, they leave, 

 like the rays of the spectrum, a picture colored of the same shades as they 

 themselves possess. 



But this same substance, when subjected to the influence of heat or 

 light before the action of the luminous rays, leads to remarkable results, 

 of which I am now about to speak. 



The action of heat modifies violet chloride of silver very much. An 

 elevation of temperature of from 212 F. to 302 F. causes a change in 



