ICO ANNUAL OF SCIENTIFIC DISCOVERY. 



deep-red glass, and exposed to the sun's rays for from a quarter to half an 

 hour, upon being submitted to the action of the prismatic spectrum, the 

 natural colors appear in all their beauty, and the green and yellow tints, 

 which previously were obtained with difficulty, are now bright and clearly 

 defined. Thus this great problem of photography is in a fair way of solu- 

 tion, and we may still hope to see not only the beautiful effects of light and 

 shade which we now obtain, but, combined therewith, the brilliancy of na- 

 ture's coloring. 



M. Niepce de St. Victor has also communicated to the Paris Academy of 

 Sciences a process for obtaining photographs of a red, green, violet, or blue 

 color. For red, the paper is prepared with a solution of 20 parts of nitrate of 

 uranium in 100 of water; the paper is dipped into this solution for the space 

 of about twenty seconds, and then dried by the fire, in the night time. It may 

 be prepared several days befoi'ehand. The impression is obtained in the 

 course of eight or ten minutes in the sun, or an hour or two in the shade. 

 AVhen taken out of the frame, the impression must be washed with warm 

 water, marking about 120 Q Fahrenheit, and then dipped into a solution of 

 two parts of red prussiate of potash in 100 of water, in a few minutes the 

 impression takes a fine red color; it must then be washed repeatedly until 

 the water runs off clear, and then dried. To obtain green, a red impression, 

 like that we have described, must first be obtained; it is then dipped into a 

 solution of nitrate of cobalt, and dried by the fire, without washing; after 

 which it must be fixed by dipping it for a few seconds into a solution of 4 

 parts of sulphate of iron and 4 of sulphuric acid in 100 parts of water; it is 

 then dipped once into pure water, and dried by the fire. Violet impressions 

 may "be obtained on the paper, prepared as above, with the nitrate of ura- 

 nium ; but, instead of the solution of prussiate of potassa, a solution of half 

 a part of chloride of gold in 100 parts of water is used; when the impression 

 has acquired a fine violet color, it must be washed repeatedly with pure 

 water, and dried. For blue impressions, the paper must be prepared with a 

 solution of red prussiate of potash, in the proportion of 20 parts to 100 of 

 water; the paper is then left to dry in the dark. This operation may be 

 performed several days beforehand. The impression should be taken out of 

 the frame when the parts exposed to the sun have acquired a light blue 

 tinge; it is then dipped, for about ten seconds, in a solution of bi-chloride of 

 mercury, saturated at the common temperature; after which it is washed 

 once with Avater, and a warm solution (temperature about 130 Fahrenheit) 

 of oxalic acid, saturated at the common temperature, is poured over it; it is 

 then washed three or four times with pure water, and then left to dry. 



ACCIDENTAL PRODUCTION OF COLORS IN PHOTOGRAPHS. 



BY M. MUGUET. 



M. Muguet states to the French Academy the circumstances under which 

 he obtained natural colors in a stei'eoscopic picture of ruins covered with ivy. 

 Each glass plate had been exposed twenty seconds, the sun shining brilliantly, 

 and on developing I was astonished at finding the color strongly developed; 

 the ivy was represented by a deep green tint, some old timber of trees by a 

 brown, the stones by a gray; all with colors in the highest degree varied. 

 Fixing did not alter them ; but in drying they lost their brilliancy, with the 

 exception of the green, which has remained as decided as at first. In taking 

 a second picture the same effect was produced, but with less strength. 



