Miscellmiies. 175 



this circumstance, engaged me to make some experiments upon your pre- 

 paration, in order to vary its application to the researches in which I am 

 occupied. First, I wished to know whether the change of color was in 

 any degree influenced by the paper itself; I therefore spread the sub- 

 stance on a piece of white unglazed porcelain instead of paper, taking 

 care to operate by night, and drying it each time at the fire, as you say, I 

 thus obtained a dry solid coating upon the porcelain, which I shut up in 

 a dark place until the morning. In the morning I took it out, and found 

 it of a pale sulphur yellow color : I then presented it to the daylight at 

 an open window looking north ; the weather was then very cloudy ; yet 

 no sooner had Tso presented it than already it was turned green, and 

 soon aftervv^ards it became black. I then wished to know whether the 

 preparation would succeed equally well if not dried at the fire; I there- 

 fore, in a darkened room, mixed the aqueous solution of bromide of po- 

 tassium with that of nitrate of silver ; a precipitate fell, which I spread 

 on a porcelain plate and left it to dry in the dark ; the next day I wrapped 

 it in several folds of paper, and brought it into another room to show it to 

 a friend ; but having taken off the covers in a dark corner of the room 

 in order to exhibit the original color, pale lemon yellow, instantly we saw 

 its tint become green, and I had hardly time to present it to a window 

 opening to the north before its color had passed to dark olive green, after 

 which it almost immediately became nearly black. I do not think it pos- 

 sible to find any substance more sensitive to light." Had M. Daguerre 

 or M. Niepce published their experiments at the commencement, Mr. 

 Talbot would have appeared merely as an improver of a foreign discovery. 

 We must notice here that, by possibility, this art may not be altogether 

 unknoM'n to jugglers in India. It is many years since an offer was made, 

 in our presence, by one of them, to show any gentleman his portrait taken 

 by a single look alone. The master of the house, however, deeming the 

 proposal an insult on the credulity of the company, ordered the man of 

 science to be instantly expelled with the rattan. 



II. Photographic processes, hy Andrew Fyfe,^ M. D., F. R. S. E., Sfc. 



Photography may be divided into three parts : the preparation of 

 the paper, — taking the impressions, — and preserving them. 



1. Methods of preparing the Paper- 



Though paper besmeared with solution of lunar caustic is darkened 

 by exposure to light, it is by no means sensitive ; other methods have 

 therefore been recommended for preparing it for photographic purpo- 

 ses. That originally given by Mr. Talbot is to soak it first in a weak 



* Read before Soc. of Arts Edinb. Mar. and Apr. 1839. From the New Edinb. 

 Phil. Jour. April to July, 1839. 



