390 Proceedings of the British Association. 



" On Elliptic Polarization of Light reflected from various substan- 

 ces" by Prof. Powell. The author had previously stated, that among 

 other results connected with this subject, he had observed the phenom- 

 ena of elliptic polarization in polarized light reflected from several min- 

 eral substances, in which it had not been (as far as he was aware) hith- 

 erto noticed. This inquiry bears upon the general question — to what 

 substances is the property of converting plane into elliptic vibrations, 

 in the reflected light, confined ? As far as observation has yet gone, it 

 seems restricted, in general, to metallic substances, whether pure or 

 compound ; but to this there seem to be some exceptions, and it re- 

 mains to be determined, what proportion of metal, in a compound, is 

 necessary to produce the result. 



Prof. Kane read a paper, by Prof. Draper of New York, " on a 

 Change produced by Exposure to the Beams of the Sun, in the Proper- 

 ties of an Elementary Substance.'''' Chlorine gas, which has been ex- 

 posed to the daylight or to sunshine, possesses qualities which are not 

 possessed by chlorine made and kept in the dark. It acquires from 

 that exposure, the property of speedily uniting with hydrogen gas. 

 This new property of the chlorine arises from its having absorbed ti- 

 thonic rays, corresponding in refrangibility to the indigo. The proper- 

 ty thus acquired is not transient, like heat, but permanent. A certain 

 portion of the tithonic rays is absorbed, and becomes latent, before any 

 visible effect ensues. Light, in producing a chemical effect, undergoes 

 a change, as well as the substance on which it acts : it becomes detith- 

 onized. The chemical force of the indigo ray is to that of the red, as 

 66 - 6 to 1. Our acquaintance with the constitution of elementary bodies 

 is still imperfect ; inasmuch as, in general, only those properties are 

 known which they possess after having been subjected to the influence 

 of light. — Dr. Robinson stated, what seemed to him confirmatory of 

 Prof. Draper's views as to the distinction between the tithonic and 

 luminous rays, that he had been induced to think the Daguerreotype 

 might give very exact representations of the inequalities of the lunar 

 surface. Having procured the apparatus, a plate prepared by Claudet's 

 process was exposed, in the place of the image of a Cassegrainian re- 

 flector, of 15 inches aperture. The intensity of the light was such, that 

 when the image of the crater Copernicus, one of the brightest in the 

 moon, came into the field of view, it dazzled the eye ; but though the 

 telescope was carried by a clock-movement of extreme precision, after 

 an exposure of half an hour there was shown, after mercurializing, but 

 a faint and indistinct image, or rather trace. Another plate, similarly 

 prepared, gave, in half a minute, on a cloudy day, a most perfect pic- 

 ture of his house, in which minute details were shown by the micro- 

 scope. Dr. R. inferred, that as the heat accompanying the solar rays 

 was not found in the light of the moon, being probably absorbed there, 



