AMERICAN INSTITUTE. 691 



sensitive to light, like the glass or paper employed in the ordi- 

 nary photographic processes, and the image of any object is thus 

 impressed upon the block with greater accuracy than it is possi- 

 ble to accomplish by human skill. So say those interested, but I 

 doubt it. 



Can any plan be devised of remedying the evil caused by froth 

 in many fluids used by the photographer, even when they are 

 viscid 1 



Can photographic paper be prepared of materials so pure as to 

 be entirely exempt from metallic dots, holes, or blemishes of any 

 kind, of one thickness, and both sides similar 1 



Monsieur Niepce De St. Victor, communicated to the French 

 Academy of Sciences, on the 16th of November last, a new and 

 remarkable photographic phenomena, to wit : that any body, after 

 having been exposed to light, retains in darkness some impression 

 of this light. Monsieur Niepce remarks : the phosphorescence 

 and the fluorescence of bodies are well known ; but I am not 

 aware that any experiments have ever been made on the subject 

 which I am about to describe. 



Expose to the direct rays of the sun, during a quarter of an 

 hour at least, an engraving, which has been kept many days in 

 obscurity, and of which one half has been covered by an opaque 

 screen; then apply this engraving upon a very sensitive photo- 

 graphic paper, and, after twenty-four hours contact in darkness, 

 we shall obtain, in black, a reproduction of the white parts of the 

 engraving, which, in the process of insulation, has not been shel- 

 tered by that screen. 



If the engraving has been kept for many days in profound 

 darkness, and we then apply it upon sensitive paper, without 

 having previously exposed it to light, it is not reproduced. 



If an engraving is exposed to the rays of the sun, for a very 

 long time, it becomes saturated with light, and the intensity of 

 the impressions obtained by contact in darkness, is so great, that 

 eventually proofs of sufficient vigor to form an original, from 

 which impressions maybe taken, will be made; thus giving us an 

 entirely new mode of reproducing engravings. 



If, after having exposed an engraving to the light during one 

 hour, we apply it upon a white card which has remained in dark- 



