Dr Fyfe on Photography. 145 



ing on the intensity of the light, and the time it has been ex- 

 posed. Accordingly, paper besmeared with the solution is 

 darkened, but if any object be put on it, so as to prevent the 

 transmission of light, the parts covered will remain white or 

 be tinged according to the density of the object ; hence the 

 art of Fhotography. 



It is not my intention to enter on a minute detail of this 

 important process ; my remarks will be chiefly confined to the 

 description of improvements, which, I conceive, I have made 

 on it since its first announcement by Mr Talbot, to whose 

 interesting paper in the London Phil. Mag. for March of this 

 year I must refer the reader who wishes more full informa- 

 tion regarding it. This paper will be found also in the Athe- 

 naeum and in many other periodicals. 



Photography may be divided into three parts : the prepara- 

 tion of the paper, — talcing the impressions, — and preserving 

 them. 



1. Methods of preparing the papier. 



Though paper besmeared with solution of lunar caustic is 

 dai'kened by exposm-e to light, it is by no means sensitive ; 

 other methods have therefore been recommended for prepar- 

 ing it for photographic purposes. That originally given by 

 Mr Talbot is to soak it first in a weak solution of sea^-salt, and, 

 when dry, to rub it over on one side with solution of lunar 

 caustic, by which chloride of silver is formed, and adheres to 

 the paper. As thus prepared, it acquires a dark colour on ex- 

 posure to light ; the depth of colour depending on the strength 

 of the solutions ; hence it may vary from lilac to deep purple, 

 approaching to black. 



In preparing paper by this method, it is very difficult to get 

 the chloride uniformly spread over its surface, and accordingly, 

 when exposed to light, it often gives a variety of shades ; in- 

 deed, in many places, it continues white. It was this that in- 

 duced me to try the use of other salts of silver ; and the one 

 which I have found to answer best is the phosphate, procured 

 in the usual way, by the addition of phosphate of soda to the so- 

 lution of lunar caustic. In preparing the paper by this method, 

 I generally employ one part of phosphate of soda dissolved iu 



VOL. XXVI. NO. LIU. — JL'LY 1839. K. 



