Trans. N. Y. Ac. Set. 17<> May 29, 



DESCRIPTION OF TWO NEW SPECIES OF BIRDS OF THE FAMILIES 

 COLUMBID^ AND FORMICARID^. 



This paper appears in the Annals, Vol 11. , No. 11. 



Dr. Elsberg nominated as a Corresponding Member the lecturer 

 for April last, Chevalier Ernst von Hesse-Warttegg, who was 

 thereupon elected unanimously. 



Mr. RoMYN Hitchcock then read the following paper, illustrated 

 with a large number of experiments : 



RECENT advances IN PHOTOGRAPHY.. 



Perhaps it is well to introduce the subject before the Academy in 

 a practical rather than a theoretical form, since photography is a branch 

 of scientific study to which our men of science generally have given 

 but little attention. Yet it possesses great interest for the chemist, who 

 has vet to determine the decompositions which an actinic ray produces 

 in compounds sensitive to light. It affords the student of molecular 

 physics a wide field for investigation. A more profound knowledge of 

 the action of light upon the photographic film will doubtless lead to a 

 deeper insight into the nature of the actinic force itself. Already the 

 photographic plate has enabled us to study the solar spectrum far 

 beyond its visible limits at either end ; for not only has it enabled us to 

 record and estabUsh the exact position of the Fraunhofer lines beyond 

 the violet, but, more recently, the spectrum of the red and ultra red has 

 also been portrayed by an ingenious apphcation of well-known facts. 



There are three compounds of silver which may be used in the pre- 

 paration of dry plates, the chloride, the iodide and the bromide. 

 These compounds, being insoluble in water, can be formed by adding a 

 corresponding salt of an alkaH to a solution of silver nitrate. They 

 are then precipitated in very minute particles. In each of these three 

 test tubes I place a few drops ot a solution of nitrate of silver. To 

 the first one I add a chloride, which gives me a pure white precipitate 

 of chloride of silver. To the second I add a bromide, to the third 

 iodide. The silver bromide is yellow, the iodide is slightly so. 



A brief exposure to the light of day changes the color of these salts, 

 and it is this peculiarity which makes them valuable for photography. 

 Years ago, when photography was in its infancy, the problem was to 

 obtain these compounds in a sufficiently sensitive condition to be use- 

 ful. If we could collect the fine particles, which are suspended in the 

 water in those tubes, before the light has affected them, spread them in 

 a perfectly uniform layer over a sheet of paper or upon a glass plate, and 

 then allow an image to fall upon it in the camera, wherever the light 

 strikes it the color would be changed, and thus a perfect photograph of 



