18 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



the indications of the thermometer, and from some pre- 

 liminary experiments finds that the temperature of the 

 sun, alter making the correction for the absorption of the 

 terrestrial atmosphere, is 1354 Centigrade. 7 A, XL VIII., 

 230. 



THE TEMPERATURE OF THE SUN. 



\Ye have already mentioned the interesting researches of 

 Violle upon the measurements of the temperatures of the 

 heavenly bodies, and have now to record a preliminary but 

 very approximate result arrived at by him for the tempera- 

 ture of the sun, the correction being made for the absorptive 

 influence of the earth's atmosphere. lie defines the true 

 temperature of the sun as that which must be possessed by 

 a body of the same apparent diameter as the sun in order 

 that, endued with an emissive power equal to the mean emis- 

 sive power of the sun, it may emit in the same time the same 

 quantity of heat as the sun. The observations made by his 

 instrument, described in the previous note, by a method which 

 he characterizes as the dynamic method, have enabled him 

 to determine the emissive power for heat of steel after fusion, 

 just as it issues from the Martin-Siemens furnace, and he 

 finds it corresponds to a temperature of 1500 Centigrade. 

 If now we assume that the mean emissive power of the sun 

 is sensibly equal to that of steel in fusion, Ave arrive at the 

 value of 2000 Centigrade for the true temperature of the 

 sun's surface. 7 A, XLVIIL, 39C. 



REFLECTING ROWER OF THE PLANET MERCURY. 



Zollner has extended to the planet Mercury a series of 

 photometric observations similar to those made by him 

 some years ago upon the moon. The observations made, 

 upon two especially favorable evenings, gave him, for the 

 relative brightness of Jupiter and Mercury, the ratio 2.7 

 in one case, and 3.2 in the other. A comparison of the 

 peculiarities of the results for Mercury and the moon leads 

 him to the conclusion that Mercury is a planet whose su- 

 perficial condition very nearly agrees with that of the 

 moon ; that also, like the moon, it probably possesses no 

 atmosphere. The reflecting power, or albedo, of Mercury 

 is the least of all the planets, and even less than that of 



