piss Miscellanies. 171 
In the spring of 1834, Mr. Talbot began a series of experiments, with 
the hope of turning to useful account the singular susceptibility evinced 
by the nitrate of silver when exposed to the rays of a powerful light; but 
not being acquainted with the researches of former chemists on the subject, 
he commenced with the same disadvantages which had baffled the skill 
and perseverance of Sir Humphry Davy. The plan he at first proposed 
Was, to receive a well-defined shadow upon a sheet of paper covered with 
asolution of nitrate of silver, by which means the part shaded would re- 
main white, while the surrounding portion was blackened by exposure to 
the light. But he was well aware that the sketch thus obtained would re- 
quire to be protected from the rays of the sun, and examined only by an 
artificial light. ~ He had carried these inquiries to some extent, and be- 
Come possessed of several curious results before he learned the steps which 
others had taken to attain the same object: and the decided terms in 
which Sir Humphry Davy expresses his failare might perhaps have dis- 
couraged his less experienced follower, had he not fortunately already 
©onquered the difficulty which had destroyed the hopes of the former 
chemists, 
Mr. Talbot continues :—“ In the course of my experiments directed to 
that end, I have been astonished at the variety of effects which I have 
found produced by a very limited number of different processes when com- 
in various ways; and also at the length of time which sometimes 
: elapses before the full effect of these manifests itself with certainty. For 
T have found that images formed in this manner, which have appeared in 
800d preservation at the end of the twelve months from their formation, 
have nevertheless somewhat altered during the second year.” He was 
‘ induced from this circumstance to watch more closely the progress of this 
change, fearing that in process of time all his pictures might be found to 
deteriorate ; this, however, was not the case, and several have withstood 
the action of the light for more than five years. 
The images obtained by this process are themselves white, but the 
stound is differently and agreeably colored ; and by slightly varying the 
Proportions, and some trifling details of manipulation, any of the following 
Ors Were readily obtained :—light blue, yellow, pink, brown, black, and 
* dark green nearly approaching to black. 
The first objects to which this process was applied were leaves and 
flowers, Which it rendered with extraordinary fidelity, representing even 
the veins and minute hairs with which they were covered, and which 
wit frequently imperceptible without the aid of a microscope. — Mr. Tal- 
bot Ses on to mention that the following considerations led him to con- 
felve the possibility of discovering a preservative process. Nitrate of sil- 
Yer, which has become darkened by exposure to the light, is no longer the 
“ame chemical substance as before; therefore, if chemical re-agents be 
*Pplied to a picture obtained in the manner already mentioned, the dark- 
