140 ANNUAL OF SCIENTIFIC DISCOVERY. 



that, by its experimental determination, the way is opened for the solu- 

 tion of many interesting- questions, such as the height of isolated 

 clouds, the relative intensity of the bright and dark portions of the 

 moon, the comparative intensity of the sun and the earth, -whether the 

 terrestrial hemispheres successively visible from the moon are more or 

 less luminous as they contain more or less land and water, and a host 

 of others. In a later paper the author mentions that no sensible por- 

 tion of light is lost in the act of reflection and refraction at the first or 

 second surfaces of a plate of glass. 



REFLECTING POWETl OF THE PLANETS. 



PUOF. LEWIS R. GIBBES, in a paper presented to the American As- 

 sociation at Charleston, states that he has made various observations 

 upon the reflecting power of the planets, and, although the means and 

 opportunities of observation are necessarily imperfect and liable to 

 error, he finds that the relative reflecting power of Jupiter is three, 

 that of Mars being unity. Saturn reflects light three and a half times 

 more powerfully than Mars. Venus, as determined by observations 

 subsequent to the reading of the paper, appears to have a much less 

 reflecting power ; in fact, the power of Jupiter in this respect is four 

 times as great as that of Venus, which seems to be inferior even to 

 that of Mars. The general conclusions arrived at are, that it is 

 certain that Saturn and Jupiter reflect light more powerfully than 

 Mars, including under the term "reflecting power 7 ' all the agencies 

 at the surface of the planet that affect the light in its course from the 

 sun to the planet, and thence to the earth ; that it is probable that the 

 reflecting power is the greater the more distant the planet from the 

 sun ; that these results will serve to predict the epochs of equality of 

 light, and thus prepare for observation. 



EFFECT OF WATER ON POLARIZED LIGHT. 



M. BIOT concludes, from a series of experiments, that water near its 

 maximum of density, or near the freezing point, but still liquid, does 

 not exercise any appreciable influence 1 upon polarized light. Comptcs 

 Bendus, March 11. 



Light of the Clouds. At the meeting of the French Academy on 

 July 1, M. Arago gave an account of a balloon ascent, undertaken by 

 Messrs. Bixio and Barral for the purpose of settling various interesting 

 questions. Although they were provided with the best instruments, 

 an accident prevented them from accomplishing their objects, and 

 even put their lives in danger. They, however, attained a height of 

 5,900 metres, and traversed a cloud 3,000 metres thick, proving by 

 experiment that the light reflected from the clouds is not polarized, 

 and ascertaining that, notwithstanding the existence of a cloud of this 

 thickness, the diminution of temperature was very nearly the same as 

 Gay-Lussac found it when the sky was perfectly cloudless. At the 

 last account the same gentlemen were preparing to make another 

 ascent. 



