EDWARD ELSWORTH. 125 
salt for this purpose, but in 1839, Sir John. Herschel 
called his attention to the superior qualities of hyposul- 
phite of soda as a solvent of silver salts, and Daguerre 
immediately adopted it. 
It has ever since been used for the same purpose, and 
the hypo bath is an indispensabie adjunct of every pho- 
tographer’s dark room at the present day. 
Such was the birth of photography ! 
Thanks to the generosity of the French Government 
in giving the benefit of Daguerre’s discovery to the 
world, the process almost immediately made its ap- 
pearance in England and in America, and during the 
year 1839, the very year in which Daguerre announced 
his success, Prof. Morse, then a rising American portrait 
painter, and Prof. Draper, the well-known chemist, were 
the first to apply the new process to portraiture. The 
length of time required for a sitting however, made the 
newly acquired art, of limited practical value. 
In order that this process of Daguerre may be more 
clearly understood, reference is made to an article by 
Prof. E. A. Aikin, M.D., of the University of Maryland, 
published in the Maryland Medical and Surgical Jour- 
nal, of April, 1840, which is almost the jirst, if not the 
jirst notice of Daguerre’s discovery, published in this 
country. Prof. Aikin divides the process into five parts : 
First—Preparing the plate, 7. e., plating a thin plate — 
of copper with a thin coating of a silver solution; then 
polishing the silver surface with pumice and oil, clean- 
ing it finally with dilute nitric acid, heating, cooling 
suddenly and repeating the polishing, until the surface 
became as clear and perfect as a mirror. This part of 
the process was a very difficult one on account of the lia- 
bility to lay bare the copper, in which case the work had 
to be done over again from the beginning. 
Second—To apply the coating of iodide. This was 
75 
