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655 
Temperature of the Sun. 
investigators, I feel there is something yet to be said ; and 
the present paper is an account of experiments of a special 
character, undertaken at the expense of the Rumford fund, 
not with the hope of at once solving so arduous a problem, 
but with the wish, in this confusion of opinion, to contribute 
one or two incontrovertible faCts as material towards the 
construction of future theory. I hope to show convincingly 
that the sun’s “ effective ” temperature is, at any rate, far 
above that of any ordinarily attained in the arts (very much 
above that of melting platinum for instance), and inci- 
dentally that the law of Dulong and Petit is untrustworthy 
precisely where we need to apply it. 
If we have no formula by which to infer the temperature 
of the sun, there- remains the comparison of its radiation 
with that of a terrestrial source of high known temperature. 
Thus the late Father Secchi has measured the radiation 
from the eleCtric arc, and M. Violle that from a Siemens- 
Martin’s furnace ; but, by comparing these only with others 
made at other times on the sun, discrepant results appear 
also. Were we, however, to compare the sun directly with 
a terrestrial source of high temperature, and bringing them 
face to face find one giving more heat than the other, there 
could (with equal emissive powers) be no question but that 
the body radiating more heat was also the higher in tem- 
perature. Strange to say, this simple test has never, that 
I know, been applied to this problem* until in the experi- 
ments I am about to describe. 
We have in the arts one process which gives what we 
want ready to hand in the production of a vertically dis- 
posed surface of several square feet of a liquid metal, hotter 
than melted platinum itself. I refer to the Bessemer 
process now in use in several places in this country, among 
others at the Edgar Thompson steel-works, about twelve 
miles from Pittsburg. I have received every possible 
assistance from the managers of this great establishment, 
and owe my acknowledgments here for their kindness. 
As the Bessemer process may be as vaguely known to 
some as it was till lately to me, 1 will first briefly describe 
so much of it as concerns the present purpose. 
An enormous egg-shaped vessel called the “ Converter,” 
capable of holding 30,000 to 40,000 pounds of melted metal, 
is swung on trunnions so that it can be raised by an engine 
to a vertical position, or lowered so as to pour its contents 
into a cauldron. First, the empty “ converter ” is inclined, 
* Experiments with the lime and ele&ric lights made for other purposes are 
not here in question. 
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