Photography — Its History, Position, and Prospects. 159 



coating. He afterwards adopted albumen, which he preferred 

 to gelatine, because less easily soluble in water. 



In 1838, Ponton, of Edinburgh, discovered the insolubility- 

 produced in bichromate of potash by light. In 1853, Talbot found 

 that organic matter in contact with it became insoluble in the 

 same circumstances. In 1855, Poitevin applied this fact to litho- 

 graphy. In 1859, Asser, of Amsterdam, invented the mode of 

 " transference," founded on the facility with which printer's ink 

 spread on gelatinized paper, may be removed by water ; and 

 in the same year, Gibbons discovered a method of producing 

 the picture from a negative directly on the stone. 



Many persons claim the merit of suggesting waxed paper, 

 as a very transparent material for negatives. Many, also, are 

 mentioned, as having first used collodion, the applicability of 

 which to photography was made known simultaneously in 

 France and England, in 1851. In that year, a report became 

 prevalent that a clergyman of the United States, named Hill, 

 had found out a means of reproducing the natural colours of 

 objects. Incredible sums were realized by the sale of books, 

 which appeared in succession — being paid for by the sub- 

 scribers in advance, and which, it was promised, would reveal 

 the important secret, but they gave no clue whatever to it. 

 Yarious efforts were then made to obtain the desired informa- 

 tion by energetic means, but without success ; and the " Hillo- 

 type" sunk at length into oblivion. Nevertheless, the repro- 

 duction of colour is not impossible, and " Heliochromy" has 

 already advanced so far as to constitute a recognized though, 

 as yet, little more than a future branch of photography. 



We are indebted to M. Edmond Bequerel for a knowledge 

 of the fact that a silver plate acquires, by immersion in a solu- 

 tion of chlorine, the property of reproducing the colours of 

 the spectrum. The effect, however, is but transitory ; since it 

 vanishes at once under the influence of white, and gradually 

 under that of coloured light. Fixation, therefore, so long the 

 desideratum of photography, is at present the great object of 

 search in heliography. But something has been done already, 

 even in this direction. In 1861, Niepce de Saint Victor 

 announced that, if the problem of fixation was not solved, 

 there was reason to expect its solution. In his laboratory at 

 the Faubourg St. Martin, he made the important discovery 

 that the different colours give rise to absorption of the vapour 

 of iodine, in different degrees. He found also that, when a 

 silver plate is plunged into a solution of chlorine, the strength of 

 which is regulated, an}' particular colour may be made to appear 

 on the plate. The least possible quantity of chlorine allows the 

 reproduction of yellow; progressively larger quantities, give 

 green, blue, indigo, violet, red, orange — the last, appearing 



