140 ANNUAL OF SCIENTIFIC DISCOVERT. 



sensitized paper turns with the action of the ship, and as the nee- 

 dle remains perfectly steadj^, every deviation or alteration of the 

 course is photographed on the paper. 



PRODUCTION OF NATURAL COLORS BY PHOTOGRAPHY. 



M. Niepce de St. Victor has recently communicated to the 

 French Academic des Sciences the results of his latest researches, 

 having for object to obtain and fix the colors of nature by means 

 of photography. His paper is full of very important, new, and in- 

 teresting facts, proving that the fixation of natural colors on the 

 photographic tablet as a practicable and available result, which for 

 a long time has been considered as a dream, is not perhaps so far 

 from being fully realized, not as a mere scientific experiment, 

 but as the completion of the splendid discovery of photography. 



The process of M. Niepce de St. Victor may be shortly described 

 as follows : The silver plate must first be chlorurized, and then 

 dipped into a bath containing 50 centigrammes of an alcoholic 

 solution of soda for every 100 grammes of water, to which a small 

 quantity of chloride of sodium is then added. The temperature 

 of the bath is raised to about 60 C., and the plate is only left in 

 for a few seconds, the liquid being stirred all the time. The plate 

 being taken out, it is rinsed in water and then warmed until it 

 acquires a bluish-violet hue, which is probably produced by the 

 reduction of a small quantity of chloride of silver. The plate is 

 now coated with a varnish composed of dextrine and chloride of 

 lead. In this way all the colors of the original, including white 

 or black of more or less intensity, are reproduced, according as 

 the plate has been prepared, and as the blacks of the copy are 

 either dull or brilliant. The reduction of the chloride should not 

 be too great, because otherwise nothing but pure black or pure white 

 could be obtained ; and in order to avoid this inconvenience a 

 little chloride of sodium is added to the soda bath. A few drops 

 of ammonia will produce the same effect. By this process a 

 colored drawing, representing a French guardsman, was repro- 

 duced by M. Niepce, with the exception of one of the black 

 gaiters, which he had cut out and replaced with white paper. 

 The black hat and the other gaiter produced a strong impression 

 on the plate, while the white gaiter was perfectly reproduced in 

 white. Much more intense blacks may be obtained by previously 

 reducing the stratum of chloride of silver by the action of light; 

 but then all the other colors lose their brilliancy in proportion. 



This production of black and white is a considerable step in 

 heliochromy. It is' a most curious and interesting fact, for it 

 would prove that black is not entirely the absence of light, but is 

 a color of itself, producing its own effects, as well as the other 

 colors. This was illustrated by the experiment made at the sug- 

 gestion of M. Chevreul, whose researches on the contrast and 

 effect of colors are so instructive and interesting. Accordingly, 

 M. Niepce tried to represent on his plate the black produced by 

 the absence of light in a hollow tube. But the hole produced no 

 effect, or rather it was negative, which is not the case when the 



