130 THE PROGRESS OF PHOTOGRAPHY. 
plate, which is less than a dozen years old, but which has 
completely revolutionized the art of photography, and 
already made possible achievements which the earlier 
photographers could not have dreamed of. If you ask 
who discovered or invented it, I point to the long list of 
the names of those industrious investigators, from Le 
Gray to Dr. Maddox, who each contributed something ; 
some by failures,and many by successes, toward the 
grand result. It is safe to say that the gelatine bromide 
dry plate, almost universally used in making photo- 
graphic negatives to-day, is the result of no one man’s 
work. 
Having said something about other processes, I will 
now take a moment to explain what a gelatine dry plate 
of the present day is. 
As its name implies, it is a sensitized gelatine film. 
Gelatine had been suggested as a medium for the reten- 
tion of the salts of silver upon the surface of glass or 
paper by Le Gray in 1850, and had been used by many 
experimenters with varied success. Of these, M. Gau- 
din, a French photographer, seems to have first 
recognized the necessity for some sensitive mix- 
ture which could always be ready for use by 
pouring it upon plates, and using them at once, 
or drying them and preserving them for future 
use. He was one of those who directed his efforts toward 
the discovery of such a mixture as early as 1853, and 
continued his experiments until 1861, when he produced 
what was known as photogene, a sensitive mixture for 
coating plates, in which both collodion and gelatine were 
used in emulsion. The use of plates coated with this 
emulsion was, however, too uncertain in its results, and 
Gaudin retired from the field without having realized the 
accomplishment of his ideal. 
One difficulty with most of these early efforts appears 
to have been that collodion continued to be used in more 
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