THE 
LONDON, EDINBURGH ayn DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENGE. 
[FOURTH SERIES.] 
APRIL 1861. 
XXXVII. On a New Proposition in the Theory of Heat. 
By Professor KirncuHore*. 
— few months ago I communicated to the Society cer- 
tain observations, which appeared of interest because they 
give some information respecting the chemical composition of the 
solar atmosphere, and point the way to further knowledge on 
this subject. These observations led to the conclusion that a 
flame whose spectrum consists of bright lines is partially opake 
for rays of light of the colour of these lines, whilst it 1s perfectly 
transparent for all other light. Iu this statement we find the 
explanation of Fraunhofer’s dark lines in the solar spectrum, and 
the justification of the conclusions regarding the composition of 
‘the sun’s atmosphere; for we find that a substance which, when 
brought into a flame, produces bright limes coincident with. the 
dark lines of the solar spectrum, must be present in the sun’s 
atmosphere. ‘The fact that a flame is partially opake solely for 
those rays which it emits, was, as I stated at the time, a matter 
of some surprise to me. Since that time I have arrived, by very 
simple theoretical considerations, at a proposition from which 
the above conclusion is immediately derived. As this proposition 
appears to me to be of considerable importance on other accounts, 
I beg to lay it before the Society. A hot body emits rays of heat. 
We feel this very perceptibly near a heated stove. The intensity of 
the rays of heat which a hot body emits, depends on the nature 
and on the temperature of the body, but is quite independent of 
the nature of the bodies on which the rays fall. We feel the 
rays of heat only in the case of very hot bodies; but they are 
* Abstract of a Lecture delivered before the Natural History Society of 
Heidelberg. Communicated by Professor Roscoe. 
Phil, Mag. 8. 4, Vol. 21. No. 140, April 1861. R 
