204 FRAGMENTS OF SCIENCE. 



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, has made this determination. 

 The absorption produced by the breath freed from its moist- 

 ure, but retaining its carbonic 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 chemi- 

 cally by Dr. Frankland, and physically by Mr. Barrett, gave 

 the following results : 



Percentage of Carbonic Acid in the Human Breath. 



Chemical analysis. Physical analysis. 



4.66 4.56 



6.33 5.22 



It is thus proved that in the quantity of ethereal motion 

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

 ure 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 oxygen are just as acceptable 

 as those of a molecule of olefiant gas ; that the vibrating 

 oxygen then stands so far below the olefiant gas in radiant 



