A Manual Of Photography

62 HISTORY OF PHOTOGRAPHY. neously after it is withdrawn. But if the exposure be discon- tinued before this effect comes on, an invisible impression is the result, to develope which all that is necessary is to breathe upon it, when it immediately appears, and very speedily acquires an extraordinary intensity and sharpness, as if by magic. Instead of the breath, it may be subjected to the regulated action of aqueous vapour by laying it in a blotting-paper book, of which some of the outer leaves on botli sides have been damped, or by holding it over warm water. Many preparations, botli of silver and gold, possess a similar property, in an inferior degree ; but none that I have yet met with, to anything like the extent of that above described. These pictures do not admit of being permanently fixed; they are so against the action of light, but not against the operations of time. They slowly fade out, even in the dark ; and in some examples which I have prepared, the remarkable phenomenon of a restoration after fading, but with reversed lights and shades, has taken place. Section V.—The Amphitype. The following very remarkable process was communicated by Sir Jolin Herschel, at the meeting of the British Association at York. The process cannot be regarded as perfect, but from its beauty when success is obtained, and the curious nature of al1 its phenomena, it is deemed important to include it, in the hope of inducing some investigator to take it up. Sir John Herschel says, alluding to the processes just de- scribed, “I had hoped to have perfected this process so far as to have reduced it to a definite statement of manipulations which would insure success. But, capricious as photographic processes notoriously are, this has proved so, even beyond the ordinary measure of such caprice. * * * Paper proper for producing an amphitype picture may be prepared either with the ferro tartrate or the ferro-citrate of the protoxide or the peroxide of mercury, or of the protoxide of lead, by using creams of these salts, or by successive applications of the nitrates of the respective oxides, singly or in mixture, to the paper, alternating witli solutions of the ammonio-tartrate or ammonio-citrate of iron, the latter solution being last applied, and in more or less excess. * * * Paper so prepared and dried takes a negative picture, in time varying from half an hour to five or six hours, according to the intensity of the light ; and the impression produced varies in apparent force from a faint and hardly