irans. Ne ¥ SAGA Ses. 176 May 29, 
DESCRIPTION OF TWO NEW SPECIES OF BIRDS OF THE FAMILIES 
COLUMBIDA AND FORMICARID&. 
This paper appears in the Annals, Vol. II., No. 11. 
Dr. ELSBERG nominated as a Corresponding Member the lecturer 
for April last, Chevalier ERNst von HeEssE-WaARTTEGG, who was 
thereupon elected unanimously. 
Mr. Romyn Hircucock 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 greatinterest for the chemist, who 
has yet 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 establish 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 application 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 alkali 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 of 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 asheet 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 
