182 Miscellanies. 



first tracing is avoided. But there is no necessity for using paper, as 

 the impression may at once be communicated to the stone, which ea- 

 sily receives the phosphate, and which may therefore be prepared in 

 the same way as the papers, and the impression also taken in the usual 

 manner, after which it is traced over with the transfer ink. By this 

 process not only is a great deal of labor saved, but the representation 

 must be much more exact than when traced ; for though by the latter 

 the outline is correct, yet much is left to be afterwards filled in by the 

 eye, whereas, by the photographic process, every, even the most mi- 

 nute filament, is distinctly and accurately laid down on the stone.* 



Method of taking Impressions in which the lights and shades are not 



reversed. 



By the different methods now described for getting photographic 

 impressions, the lights and shades are always reversed, because, as it 

 is by the action of the light that the compound of silver is darkened, 

 wherever it is prevented from penetrating, the paper retains its ori- 

 ginal color. Though the impressions thus procured are accurate as to 

 outlines, yet in many cases the representation is far from being pleas- 

 ing ; it is therefore a great desideratum to have a method of getting 

 impressions in which there is no reverse ; in fact, to give a true repre- 

 sentation of the object, and in this I have succeeded by the use of the 

 iodide of potassium. I have already stated, that when the darkened 

 phosphate is exposed to the iodide, it is instantly converted to yellow, 

 provided the solution is of sufficient strength ; if weak, the action goes 

 on slowly. In some impressions which I had attempted to preserve 

 in this way, 1 observed that when exposed to light they began to fade, 

 Avhich induced me to try the eflect of light on darkened paper, soaked 

 in solution of iodide, of such strength that it just failed to attack it 

 instantly. In my first attempt I succeeded in bleaching the paper, 

 but in my next I failed. On considering the circumstances under 

 which these trials were made, I found that the only difference between 

 them was, that in the first the paper was moist, in the last it was dry. 

 Accordingly, on repeating the experiment with the paper moist, I 

 again succeeded in getting a delineation of the object placed on the pa- 

 per, as distinct and altogether as brilliant as those obtained by the 

 other process. 



* For this method of applying the photographic process I am indebted to Mr. 

 Nichol, lithographer, bj whom lithographic impressions, thus taken, were exhibited 

 to the Society of Arts. As a proof of the value of this process,! may also mention, 

 that on the evening of the 17th of April, when I exhibited a photograpiiic specimen 

 of dried ferns, it was, by Mr. Forrester, lithographed, and impressions taken from 

 it, in the course of two hours; had tliis been done in the usual way, it would have 

 required many hours of labor, and after all not have given such accurate delinea- 

 tions. 



