PHOSPHORESCENCE. 73 
black figures, wood, linen, cardboard, marble, 
etc., and always with the same result. In every 
experiment, an impression was left on the photo- 
graphic paper in the dark, and this experiment 
was clearly proved to be owing to the action of 
light alone ; no chemical agent whatever to which 
such a phenomenon might be attributed, entered 
into. these experiments. 
It was soon perceived that certain substances 
seemed to possess, as it were, “a greater affinity 
for light than others,’ and, as M. Niépce used 'to 
say, ‘“seemed to become, during their exposure 
to the sun, more saturated with ight than others” 
in the same space of time, and, consequently, acted 
with greater intensity on the photographic paper 
in the dark. 
A step more, and my friend had actually “ bot- 
tled up hight,” to use his own expression. A sheet 
of cardboard, imbibed with a solution of tartaric 
acid or a salt of uranium, was rolled into a cylinder 
and placed inside a tin tube, open at one end, so 
as to lmeit. ‘The tube was then exposed to the 
hght, with its orifice towards the sun. After a 
certain time had elapsed, from a quarter of an hour 
to about an hour, the orifice of the tube was her- 
metically sealed up. I?f such a tube be taken into 
a dark room, opened, and its orifice placed upon 
a sheet of photographic paper, in a very short 
time the impression of this orifice is left upon the 
