180 ANNUAL OF SCIENTIFIC DISCOVERY. 



obtained in twenty seconds, and Saturn was solarized in eight min- 

 utes, or one hundred and sixty seconds. The proportion of these 

 times is as one to twenty-four ; whereas, according to the law of the 

 distance, it ought to have been as one to eighty. This result he 

 considers as proving that Saturn has a reflecting atmosphere, as he 

 inferred that Jupiter had, from its superior photogenic power. 



'NOVELTIES IN PHOTOGRAPHY. 



Photography by Absorption. A singular photographic process, 

 which has been called photography by absorption, has been de- 

 scribed by M. Niepce de St. Victor, under the name of a new action 

 of light. If an engraving, which has been kept several days in the 

 dark, and exposed fifteen minutes to the sun, is kept four hours in. 

 contact with a sheet of sensitive paper in the dark, a negative pic- 

 ture of the engraving will be obtained. -If a space of one-eighth of 

 an inch, or a film of collodion or gelatine, be interposed between the 

 engraving and the sensitive paper, a picture will still be obtained ; 

 but not if a film of mica, glass, or rock crystal be interposed. In 

 order to show this action more satisfactorily, M. Niepce took an 

 opaque tube, closed at one end and lined with white paper, and hav- 

 ing exposed the. open end to the sun for an hour, he placed at that 

 end a sensitive paper, which, after twenty-four hours, exhibited a 

 negative image of the opening. The following experiment is still 

 more interesting. M. Niepce took a sheet of white paper that had 

 been long in the dark, and, having placed it in the camera, he ex- 

 posed it to a picture brilliantly illuminated b^ the sun. When it was 

 taken out and applied to a sheet of sensitive paper, there was repro- 

 duced in twenty-four hours a very visible copy of the brilliantly- 

 illuminated picture. 



This new action of light, to which M. Xiepce has given the name 

 of the persistent activity or storing up of light, is finely shown in the 

 following experiment : A negative on glass or paper is placed on a 

 sheet of paper that has been several days in the dark, and exposed 

 for a sufficient time to the sun's rays. When taken out in the dark, 

 a copy of the negative is brought out by a solution of nitrate of silver, 

 and fixed by washing in pure water. 



In continuing these important researches, M. Niepce has shown 

 that photographic pictures may be obtained from almost all chemical 

 actions. If a sheet of paper, for example, is impregnated with any 

 soluble substance, and dried in the dark, it will receive an impression 

 from a negative when exposed to the sun. This impression will be 

 developed if the picture taken out in the dark is treated with any 

 reagent capable of transforming the soluble substance, or entering 

 into combination with it. A result the reverse of this will be obtained 

 it' the paper is impregnated with the reagent and developed with the 

 soluble substance. The salts of gold and silver, the dyes of turnesol 

 and curcuma, arid iodide of potassium for common paper sized with 

 soap, are the most important reagents to be employed. If the nitrate 

 of uranium is the soluble substance, and the red prussiate of potash 

 the reagent, the picture will be of a fine blood-red color, and may be 

 iixcd by pure water. If the picture is put into a solution of any salt 



