394 FEAGMENTS OF SCIENCE. 



opaque. The platinum wire, therefore, which aug- 

 mented the radiation through the pure glass, augmented 

 the absorption of the black glass and mica. 



No more striking or instructive illustration of the 

 influence of coincidence could be adduced than that 

 furnished 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 quantity of the gas, only one-thirtieth of an 

 atmosphere in density, contained in a polished brass 

 tube four feet long, intercepts 50 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 compound gases. 

 Moreover, for the radiation from a hydrogen 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 mer- 

 cury, 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 tem- 

 perature of 20 C. and carbonic acid at a temperature 

 of over 3000 C., the periods of oscillation of both the 

 incandescent and the cold gas belonging to the ultra- 

 red portion of the spectrum. 



It will be seen from the foregoing remarks and 

 experiments how impossible it is to determine the effect 

 of temperature pure and simple on the transmission of 

 radiant heat if different sources of heat be employed. 

 Throughout such an examination the same oscillating 

 atoms ought to be retained. This is done by heating a 

 platinum spiral by an electric current, the temperature 



