6 54 
Temperature of the Sun. 
[October, 
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° C. ; Mr. Ericsson, whose 
labours on this point deserve wider recognition, is confident 
that the temperature is not materially different from 
4,000,000° F. ; Father Secchi, in his latest research, makes 
it 133,000° C. ; Sir Wm. Thomson and others estimate 
30,000° to 60,000° C. 
These extremely gross discrepancies having drawn general 
attention, many distinguished French physicists have lately 
re-investigated the subject, and, using Dulong’s and Petit's 
formula, have after most elaborate research arrived at the 
nearly unanimous conclusion that the temperature of the 
solar surface is altogether lower than any of these, — is in 
any case not more than 2000° to 2500° C., but is more pro- 
bably below than above the temperatures which are reached 
in our furnaces, and in faeft is probably less than that of 
melting platinum. 
It is here to be borne in mind that we really know nothing 
about the absolute emissive capacity of the solar surface, 
and that to simplify the problem, when we speak of the 
sun’s being at a lower temperature than that of a certain 
lamp-black surface or hot platinum or steel, it is assumed, 
for the purpose of comparison, by myself as well as by the 
above-named investigators, that both the solar and terres- 
trial sources of heat have the same emissive capacity. The 
temperature thus defined has been called the “ effective ” 
temperature. 
M. Violle, one of the most distinguished students of the 
subject, whose experiments bear evidence of intelligent care, 
found by observations at Grenoble, in March, 1874, that, 
with an emissive power thus defined, the temperature of the 
solar surface was 1230° C.* In a subsequent memoir he 
finds for the same the rather higher value of 1354° C.t 
After allowing for absorption in our atmosphere, it remains 
true that the temperature is then much below that of 
melting platinum, and this seems to be confirmed by his 
later results, which give about 1550 C. as the highest 
“ effective ” temperature. 
All these and other observations involve the use of the 
empirical formula, well known as that of Dulong and Petit, 
which has replaced the earlier and simpler one of Newton. 
Now, whatever be the apparent presumption of opposing 
my opinion to that of so many conscientious and recent 
* Comptes Rendus, vol. lxxxviii., p. 1425. 
f Id., r . 1816. 
