THE MONTHLY 
JOURNAL OF SCIENCE. 
OCTOBER, 1879. 
I. ON THE TEMPERATURE OF THE SUN * 
By Professor S. P. Langley. 
J T 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 temperature 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 in- 
organic kingdom, is accompanied by the emission or absorp- 
tion of heat, and, considering that — whether the subject of 
observation be the germination 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 com- 
plete 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 substan- 
tially 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 Pouillet, which were about 1*75 calories 
per centimetre 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 
* A Paper read before the American Academy of Arts and Sciences, October, 
1878. Communicated by the author. 
VOL. IX. (N.S.) 
2 T 
