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. Niepce used to 

 say, " seemed to become, during their exposure 

 to the sun, more saturated with light 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 light," 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 line it. The tube was then exposed to the 

 light, 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. If 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 



