A Manual Of Photography

CHAPTER VI. ON THE POSSIBILITY OF PRODUCING PHOTOGRAPHS IN THEIR NATURAL COLOURS. Few speculations are more replete with interest than that of the probability of our succeeding in the production of photographic images in their local colours. M. Biot, a great authority, says,— “ Substances of the same tint may present, in the quantity, or the nature of the radiations which they reflect, as many diversities, or diversities of the same order, as substances of a different tint; inversely, they may be similar in their property of reflecting chemical radiations when they are dissimilar to the eye ; so that the difference of tint which they present to the eye may entirely disappear in the chemical picture. These are the difficulties in- herent in the formation of photographic pictures, and they show, I think, evidently, the illusion of the experimenters who hope to reconcile, not only the intensity, but the tints of the chemical impressions produced by radiation, with the colours of the objects from which these rays emanate.” It may be remembered'that two years since, Sir John Herschel succeeded in procuring upon photographic paper a coloured image of the solar spectrum ; and that eminent inquirer has communicated to me a recent discovery of great interest, which I have his permission to publish. “I have got specimens of paper,” says Sir John Herschel, *‘ long kept, which give a considerably better representation of the spectrum in its natural colours than I had obtained at the date of my paper (February 1840), and that light on a dark ground; but at present I am not prepared to say that this will prove an available process for coloured photographs, though it brings the hope nearer.” Here we have the speculations of one philosopher representing the production of such pictures as hopeless, while the experiments of another prove these to be within the range of probabilities. My own experiments have, in many instances, given me coloured pictures of the prismatic spectrum, dark upon a light ground, but the most beautiful I have yet obtained has been upon the daguerreotype iodidated tablets, on which the colours