MEMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. 



155 



then removed ; then ten strong sparks were passed over 

 the spar, each of which made it emit an emerald light ; 

 but during the moment of the passage of each spark a 

 screen was interposed, that no direct or reflected light, 

 and, indeed, none but that of the phosphorus, could reach 

 the mirror and sensitive plate. 



On mercurializing, it was found as before that the 

 lamp was beautifully depicted but the spar was invisible. 



In Fig. 19, a is the oil-lamp, b the white paper, c the 

 chlorophane, cut and polished, d the contact - breaker 

 with its wires,// the concave mirror. Its concavity 

 faces the above-named objects, and reflects their images 

 inverted and reversed on a sensitive plate, e. The mir- 

 ror and sensitive plate are enclosed in a darkened box 

 not shown in the figure. 



Fig. 19. 



Estimated, therefore, by the chemical effects they can 

 produce, the light from chlorophane is incomparably less 

 intense than that from a common lamp. For there can 

 be no doubt that each of the ten Leyden sparks gave a 

 light which made the spar phosphoresce brilliantly for six 

 seconds, and the whole phosphorescence was equal in du- 

 ration to that produced by the light of the lamp; yet the 

 latter had changed the plate to a maximum, while the 

 former had not made the smallest perceptible impression. 



As the foregoing attempt to obtain photographic ef- 



