154 ANNUAL OF SCIENTIFIC DISCOVERY. 



from a lamp fed with alcohol containing; chloride of sodium. Liquid wax 

 or stcarine poured on the surface will receive an impression of even the 

 finest unevenness, only discernible with the glass, and therefore also stria} 

 causing the iridescense. That the surface of mother-of-pearl gives this opal- 

 ' - -i-'.ice, in a number of positions, to the eye, and that obtained on wax only 

 when held in a certain direction, is caused by the many laminae underlying 

 each orher in the original, as remarked by Breithaupt. Seen through a 

 Nieol's prism (of course with homogeneous light), in case the undulat- 

 ing plane of the prism falls vertically upon that of the reflected rays, the 

 surface of the wax impression appears dark, while that of the original will 

 still be bright; for although the plane of the prism be vertical to that of 

 the rays proceeding from the surface, it intersects those from the underlying 

 laniinte under a different angle. Archiv. der Pharmacie, 18-39. 



NEW PHOTOMETER. 



The following is a description of a new photometer, recently introduced 

 for the testing of coal-gas. 



It consists simply of a disk of paper, one portion of which is oiled and 

 rendered translucent, while the remainder is left unoilecl and opaque. The 

 disk slides on a long graduated bar, which has the standard spermaceti can- 

 dle (burning one hundred grains an hour) at one end, and the standard gas- 

 burner (a five-feet Argand burner, fifteen holes, one-twenty-third of an inch 

 in diameter, seven-inch chimney) at the other. If the paper is placed very 

 near the candle, on looking at the side next the candle, we see the opaque 

 portion of the disk much brighter than the oiled portion, the quantity of 

 light from the candle which is reflected being greater than the quantity 

 from the gas which is transmitted. On looking at the other side of the 

 paper, the oiled portion presents the brighter appearance. The paper is 

 slipped along until the distinction between the oiled and opaque parts disap- 

 pears, and all portions of the disk present a uniform brightness, when seen 

 on both sides. The comparative distances between the paper and the can- 

 dle, and the gas and paper, being measured by the graduated bar on which 

 the paper slides, a simple calculation gives the quantity of light emitted by 

 the gas as compared with the candle. 



ON THE MEASUREMENT OF THE CHEMICAL ACTION OF LIGHT. 



M. Niepce St. Victor has devised the following plan for measuring the 

 chemical action of light. He fills a flask with a solution composed of 

 oxalic acid and nitrate of uranium, which produces, under the action of 

 even diffused light, a disengagement of carbonic acid gas with efferves- 

 cence. In order to assure himself that heat has nothing to do with this 

 phenomenon, the vessel containing the solution was placed in a bath, and 

 heated to the boiling-point, but no disengagement of gas took place. 



There is in this fact the principle of an apparatus for measuring, compara- 

 tively, the action of light. A graduated tube, passing across the stopper 

 of the flask, receives the liquid, which, under the pressure of the gas disen- 

 gaged, rises more or less, according to the power of the luminous rays, 

 during a given space of time. 





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