THE RISE AND PROGRESS OF PHOTOGRAPHY. 149 
Other plates were quickly prepared, exposed, and put in the yee 
board; result, the same. Thus mercurial vapour became the 
recognized medium for development in this process. 
The news of his discovery soon spread, and Humboldt, Biot, 
Arago, and others became his confidants. After much persuasion 
0 give 
the news of this wonderful process of picture-making had been 
th 
all the élite of art, science, and even diplomacy, resident at that 
time in Paris. Arago, in his opening speech, says, “ France has 
adopted the discov 
world.” In 
giving a body to the impalpable and fugitive image of objec 
reflected in the retina of the eye, in a mirror, in the apparatus 
the sitters were obliged to be placed in the sun; 
To >i you some idea of the patience required in posing in 
those days, I have taken an extract from Gaston Tissan sec eae 
says :—“ The model took a graceful attitude, resting o 
ne 
on the back of a chair, and looking as amiable as one could do 
