HISTORY OE^ PHOTOGRAPHY. l7l 



velops itself spontaneously, and at length becomes very intense. 

 But if the paper be thoroughly dried in the dark (in Avhicli state it 

 is of a xevy pale greenish-yellow color) it possesses the singular prop- 

 erty of receiving a dormant or invisible picture, to produce which (if 

 it be, for instance, an engraving that is to be copied), from thirty 

 seconds' to a minute's exposure in the sunshine is requisite. It should 

 not be continued too long, as not only is the ultimate effect less strik- 

 ing, but a picture l)egins to be visibly produced, which darkens spon- 

 taneously after it is witlidrawn. But if the exposure be discontinued 

 before this effect comes on an invisibl-e impression is the result, to de- 

 velop which all that is necssary is to breathe upon it, when it imme- 

 diately appears, and very speedily acquires an extraordinary inten- 

 sity and sharpness as if by magic. Instead of the breath it may be 

 subjected to the regulated action of aqueous vapor by laying it in a 

 blotting-paper book of which some of the outer leaves on both sides 

 have been dampened, or by holding it over warm water. 



Many preparations, both of silver and gold, possess a similar prop- 

 erty in an inferior degree, but none that I have yet met with to any- 

 thing 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. 



THE AMPHITYPE. 



The following very remarkable process was communicated by Sir 

 John Herschel at the meeting of the British Association at York. 

 The process can not be regarded as perfect, but from its beauty when 

 success is ol^tained and tlie curious nature of all its phenomena it is 

 deemed important to include it in the hope of inducing some investi- 

 gator to take it up. 



Sir John Herschel says, alluding to the processes just described: 



I had hoped, to have perfected this process so far as to have reduced it to a 

 a definite statement of uianipuhitions which would insure success. But capri- 

 cious as photographic processes notoriously are, this has proved so even beyond 

 tliGordiniiry nieusureof such (•a[>i"it'e. * * * Paper proper for producing an auiphi- 

 type picture may be prepared either with the ferrotartrate or the ferrocitrate 

 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 with 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 perceptible picture to one of 



