A. MATHEMATICS AND ASTRONOMY. 17 



the temperature of the sun, the radiation of the sky border- 

 ing the sun, and the general absorption of the solar atmos- 

 phere. 7 A, XLVIIL, 158. 



VARIABILITY OF SOLAR TEMPERATURES. 



Mr. Blandford, of Calcutta, gives the results of his studies 

 into the variability of solar temperatures as indicated by the 

 maximum black bulb in vacuo solar thermometer. Mr. Bland- 

 ford's investigations are based upon observations made from 

 1868 to 1874 at stations in India, and his results seem very 

 striking, if not absolutely conclusive, as to the direct varia- 

 tion of the solar heat with the number of the spots and prom- 

 inences. The absolute maximum temperature of the sun 

 seems, according to his diagram, to have been reached in 

 February, 1871. Unfortunately the highest sun tempera- 

 tures recorded by his thermometers occurred not on days 

 that were cloudless, with a very dry atmosphere, but on those 

 in which there was a considerable proportion of cloud and 

 frequent rains. The effect of the heat reflected from the 

 edges of the cumulus clouds upon his thermometers seems 

 not to have been duly considered by him. 



THE TEMPERATURE OF THE SUN. 



An improved method of investigation to determine the 

 temperature of the sun has been put in execution by Violle, 

 who describes his apparatus as consisting essentially of two 

 concentric and spherical envelopes of brass. In the centre 

 of the interior one is the bulb of the thermometer, while be- 

 tween the two envelopes a continuous current of water cir- 

 culates. The exterior surface is highly polished, while the 

 interior surface of the interior sphere is covered with lamp- 

 black. The experiment is conducted by first determining 

 the temperature shown by the interior thermometer without 

 exposure to the sun and then the temperature as shown dur- 

 ing the exposure to the sun and after it has become station- 

 ary under the influence of the solar rays. The conclusions 

 that can be drawn from this apparatus depend upon the em- 

 ployment in succession of different thermometers and differ- 

 ent apertures of the diaphragm which allows the solar rays 

 to fall upon the thermometer. Violle has made a very care- 

 ful investigation into all the influences which can affect 



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