CONTRIBUTIONS TO MOLECULAR PHYSICS 415 



50 per cent of the radiation from a hydrogen flamo 

 through a layer of carbon which intercepted the light of 

 an intensely brilliant flame. The products of combustion 

 of alcohol are carbonic acid and aqueous vapor, the heat 

 of which is almost wholly ultra-red. For this radiation, 

 then, the carbon is in a considerable degree transparent, 

 while for the radiation from the platinum spiral it is in 

 a great measure opaque. The platinum wire, therefore, 

 which augmented the radiation through the pure glass, 

 augmented the absorption of the black glass and mica. 



No more striking or instructive illustration of the in- 

 fluence of coincidence could be adduced than that fur- 

 nished by the radiation from a carbonic oxide flame. 

 Here the product of combustion is carbonic acid; and on 

 the radiation from this flame even the ordinary carbonic 

 acid of the atmosphere exerts a powerful effect. A quan- 

 tity of the gas, only one-thirtieth of an atmosphere in 

 density, contained in a polished brass tube four feet long, 

 intercepts 60 per cent of the radiation from the carbonic 

 oxide flame. For the heat emitted by lampblack, olefiant 

 gas is a far more powerful absorber than carbonic acid; 

 in fact, for such heat, with one exception, carbonic acid 

 is the most feeble absorber to be found among the com- 

 pound gases. Moreover, for the radiation from a hydro- 

 gen flame olefiant gas possesses twice the absorbent power 

 of carbonic acid, while for the radiation from the carbonic 

 oxide flame, at a common pressure of one inch of mercury, 

 the absorption by carbonic acid is more than twice that 

 of olefiant gas. Thus we establish the coincidence of 

 period between carbonic acid at a temperature of 20° C. 

 and carbonic acid at a temperature of over 3,000° 0., 

 the periods of oscillation of both the incandescent and 



