106 PROCEEDINGS OP THE AMERICAN ACADEMY 



Investigations on Light and Heat, made and published wholly or in part with 

 appropriation from the Rumford Fund. 



VII. 



ON THE TEMPERATURE OF THE SUN. 

 By Professor S. P. Langley. 



Presented Oct. 9, 1878. 



It is known to all that there is a problem of the highest interest in 

 solar physics at present waiting solution : I mean that of the temper- 

 ature of the sun ; and, so far as the whole radiant energy is inferable 

 from the rate of emission of heat, the problem is one the theoretical 

 solution of which is evidently dependent on our knowledge of the 

 laws of cooling. 



Every operation of Nature, whether in the organic or inorganic 

 kingdom, is accompanied by the emission or absorption of heat ; 

 and, considering that, whether the subject of observation be the germi- 

 nation of a seed, the heat of a stove, or the outflow from the sun upon 

 the planetary system, we want to know the rate of the deperdition of 

 energy, one might certainly suppose that no physical law would have 

 been better ascertained ; but we are here, however (at least in regard 

 to high temperatures), in a state of nearly complete ignorance, and 

 know almost literally nothing about what so intimately concerns 

 us. This is a reproach to modern physics, which has probably made 

 no real advance here since Newton. To justify this language, I 

 remark that, in the case of the solar temperature, the amount of heat 

 the sun sends us is scarcely in question, as we are all substantially 

 agreed on the way to measure this and on the results of measurement. 

 The latest of these give, it is true, larger values than those of Pouil- 

 let, which were about 1.75 calories per centimeter per minute instead 

 of 2.50 ; but these considerable variations are so trifling compared 

 with those in the deductions made from them, that we may still say 

 there is substantial agreement as to data. From like data, then, Sir 

 John Herschel concludes that the temperature of the solar surface is 

 over 5,000,000° centigrade ; Mr. Ericsson, whose labors on this 

 point deserve wider recognition, is confident that the temperature is 



