V2 
CHAPTER VII. 
INVISIBLE PHOSPHORESCENCE. 
I wave given the name of Invisible Phosphores- 
cence to some curious phenomena discovered by 
my ingenious friend M. Niépce de St. Victor, 
who communicated them to me with much kind- 
ness before they were published. During latter 
years he has, however, addressed to the Academy 
of Sciences, at Paris, a number of notes and papers, 
in which his experiments are detailed.* The basis 
of them all was the following interesting obser- 
vation :— 
M. Niépce discovered that if an engraving be 
exposed for some time to the sunlight, and then 
taken into a dark room, and placed upon a sheet 
of photographic paper prepared with chloride of 
silver, an impression of the engraving is produced 
in a very short space of time upon the paper. This 
experiment was immediately tried with a great 
variety of substances, such as white porcelain with 
* ‘Comptes-Rendus’ from 1857 to the present time. 
