AMERICAN INSTITUTE. 693 



will be reproduced by the radiations which have been absorbed, 

 and re-develcped from the interior of the tube." 



If we close the tube hermetically as soon as we cease to ex- 

 pose it to the light, we shall preserve, during an indefinite time, 

 the faculty of radiation, which the insulation has communicated. 



Keep a piece of card sometime in darkness, then place it in 

 a camera; obscure for three hours, and on it project an image 

 illuminated by the sun; then apply the card to sensitive paper, and 

 after twenty-four hours there will be a reproduction of the 

 primitive image of the camera-obscura. Monsieur Niepce has 

 made several experiments with substances possessing the quality 

 of fluorescence. For example, he traced a design upon a sheet 

 of white paper with a solution of sulphate of quinine, which is 

 one of the most fluorescent bodies; the paper was then exposed 

 to the sun, and subsequently applied to the sensitive paper. The 

 fluorescent parts were reproduced in black, much more intense 

 than that of the paper upon which the design was formed. A 

 plate of glass interposed between the design and the sensitive 

 paper prevented any impression. Trace a design with phospho- 

 rus upon paper, without exposing it to light, and it will impress 

 sensitive paper. This is due to the formation of phosphide of silver. 



Mr. I. Mercer describes a new process, by Calotype, in which 

 the agent employed is the peroxalate of iron, when, by the sub- 

 sequent application of different re-agents, photographic pictures 

 of the most varied and even brilliant colors are produced. 



Mr Joseph Dixon, of Jersey City — Mr. Hill has long pretended 

 to obtain the natural colors by the camera. Some approximations 

 only have been gaiued, the general tints not gained; and so far 

 Mr. Hill has played the part of that distinguished insect, the 

 humbug. He has been offered a fortune for the invention if true. 

 He could have received for it one hundred thousand dollars at 

 any time. 



Mr. Seeley remarked that the extent of Mr. Hill's colors on 

 metallic plates was red, green and blue, but on the whole Mr. S. 

 thought the term humbug the true one. 



Subject for next meeting, " Photography and Light." 



Adjourned. H. MEIGS, Secretary. 



