A Manual Of Photography

174 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. is yellow, and cuts off nearly all the “ chemical” rays, allowing only of the free passage of the less refrangible rays ; the most abundant being the yellow. This retards the process of solariza- tion, but it produces its complementary colour on the plate. These facts will, I think, prove that the possibility of our being enabled to produce coloured photographs is decided, and that the probability of it is brought infinitely nearer, particularly by Sir John Herschel’s very important discovery, than it was supposed to be... M. Edmond Becquerel has recently succeeded in obtaining bright impressions of the spectrum in colours, and copying highly coloured drawings on metallic plates prepared with chlorine. Mr Hill of New York, announced that he had obtained more than fifty pictures from nature in all the beauty of native colour- ation This process was not disclosed, but we were assured that it was a modification of the daguerreotype—one material, quite new being introduced—and that as soon as the manipulatory details were perfected the whole was to be published. 2 very long time has elapsed, and we have no indication of any develop- ment of his method of operating, and I believenone of his specimens have reached England. The results of M. Niepce de St-Victor have been of a far more satisfactory character: the main particulars thereof we select from a memoir entitled “Upon the Relation existing between the Colours of certain coloured 1 lames with the Heliographie Images coloured by Light.” When a plate of silver is plunged into a solution of sulphate of copper and chloride of sodium, at the same time that it is rendered electro-positive by means of the voltaic battery, the chloride formed becomes susceptible of colouration, when, having been withdrawn from the bath, it receives the influence of ^yp Niepce de St.-Victor, from observing that when chloride of sodium (common salt) was employed the plate became more susceptible of receiving a yellow colour than any other, and knowing that it imparted a yellow colour to flame, was led to believe that a relation existed between the colour communicated by a body to flame, and the colour developed upon a plate of silver, which should have been chloridated with the particular To avoid complexity, it may be briefly stated that the bath in which the sensitive surface is obtained is prepared with water, holding free chlorine in solution, to which lias been added the salt which is essential to give a predominance to any particular colour. . . ,.„ It is well known that strontian gives a purple colour to flames