692 TRANSACTIONS OF THE 



ness during some days, and if, after having left the engraving id 

 contact with the card during twenty-four hours, we put the card 

 in its turn in contact wath a leaf of sensitive paper, we shall have 

 after twenty-four hours of this new contact, a reproduction of the 

 engraving. 



When a tablet of black marble, lightly strewn with white spots, 

 after having been exposed to the light, is applied at once to a sensi- 

 tive paper, the white parts of the marble only will be imprinted 

 upon the paper. 



When a black and white feather has been exposed to the sun, 

 and applied in darkness to a sensitive surface, the white parts 

 alone imprint their image. 



The feather of a parrot, red, green, blue, and black, has given 

 scarcely any impression, acting as if the feather had been black. 

 Experiments have been made with textile fabrics of diflferent na- 

 tures and of various colors. The following are a few of the results : 

 Cotton — White, impressed the sensitive paper. 



" Brown, (by madder and alumina.) Nothing given. 



" Violet, (by madder, alumina, and iron.) Scarcely any- 



thing. 



" Red, (by cochineal.) Nothing. 



" Turkey red, (by madder and alum.) Nothing. 



" Prussian blue, upon white ground, is the blue which 



produces the best impression. 



" Blue, (by indigo.) Nothing. 



" Chamoois, (by peroxide of iron.) No impression. 



Linen, silk, and woolen cloths give equally diflferent impres- 

 sions, according to the chemical nature of the colors. Mr. 

 Niepce says : 



" If we take a tube of metal, of tin plate, or any opaque sub- 

 stance, and close one end, and cover the interior with white 

 paper. Then expose the open end for an hour and ten minutes 

 to the sun's rays. After which place the open end on a sheet of 

 sensitive paper, and let it remain in that state for one day and 

 night, the image of the circumference of the tube will have been 

 designed. More than this. If an engraving upon China paper 

 is interposed between the tube and the sensitive paper, the same 



