50 FRA OMENTS OF SCIENCE. 



olefiant gas. This wonderful change in 'the power of the 

 former, as an absorber, is simply due to the fact that the 

 periods of the hot and cold carbonic acid are identical, and 

 that the waves from the flame freely transfer their motion 

 to the molecules which synchronize with them. Thus it is 

 that the tenth of an atmosphere of carbonic acid, enclosed 

 in a tube four feet long, absorbs 60 per cent, of the radia- 

 tion from a carbonic oxide flame, while one-thirtieth of an 

 atmosphere absorbs -18 per cent, of the heat from the same 

 source. 



In fact, the presence of the minutest quantity of car- 

 bonic acid may be detected by its action on the rays from 

 the carbonic oxide flame. Carrying, for example, the dried 

 human breath into a tube four feet long, the absorption 

 there effected by the carbonic acid of the breath amounts 

 to 50 per cent, of the entire radiation. Radiant heat may 

 indeed be employed as a means of determining practically 

 the amount of carbonic acid expired from the lungs. My 

 late assistant, Mr. Barrett, while under my direction, 

 made this determination. The absorption produced by 

 the breath freed from its moisture, but retaining its car- 

 bonic acid, was first determined. Carbonic acid, artificially 

 prepared, was then mixed with dry air in such proportions 

 that the action of the mixture upon the rays of heat was 

 the same as that of the dried breath. The percentage of 

 the former being known, immediately gave that of the 

 latter. The same breath, analyzed chemically by Dr. 

 Frankland, and physically by Mr. Barrett, gave the follow- 

 ing results: 



Percentage of Carbonic Acid in the Human Breath. 

 Chemical analysis Physical analysis 



4.66 4.56 



5.33 5.22 



It is thus proved that in the quantity of ethereal motion 

 which it is competent to take up, we have a practical 

 measure of the carbonic acid of the breath, and hence of 

 the combustion going on in the human lungs. 



Still this question of period, though of the utmost im- 

 portance, is not competent to account for the whole of the 

 observed facts. The ether, as far as we know, accepts 

 vibrations of all periods with the same readiness. To it 

 the oscillations of an atom of free oxygen are just as 



