342 Prof. Tyndall on the Absorption and 



In the foregoing experiments dry air was used to warm the 

 vapours, but similar differences ought to be exhibited by gases 

 when heated by their own dynamic action. This is the case, as 

 the following experiments show : — 



Table VI. — Dynamic Radiation of Gases. 



Name. Radiation. 



Air . . 7 



Oxygen 7 



Hydrogen 7 



Carbonic oxide 19 



Carbonic acid 21 



Nitrous oxide 31 



defiant gas . . . . . 63 



I also satisfied myself of the energetic radiation of the two fol- 

 lowing gases, which, however, were used in irregular quantities. 

 They were admitted into the tube from a large bolthead, until a 

 common tension was established between the gas in the tube and 

 the gas in the bolthead. 



Radiation. Absorption. 

 o o 



Ammonia 15 in. tension . . . 56'5 33*5 



Sulphurous acid 16 in. tension . 45 24 



Let us reflect for an instant on the condition of our tube with 

 its J inch of vapour at the moment when the latter has been 

 heated by the entrance of the air. The gaseous column is heated 

 throughout to the same temperature; the elastic condition of 

 the luminiferous ether is the same for all the particles, and con- 

 sequently their periods of vibration are all the same. Hence 

 each molecule is in that precise condition which enables it to 

 absorb most effectually the undulations emanating from its 

 neighbours. The rays from the particles at the end of the tube 

 most distant from the pile have to cross a space of nearly 3 feet 

 before they reach the latter, this space being partially filled with 

 molecules circumstanced as just described. Hence absorption 

 to a comparatively greater extent must occur ; and indeed we 

 can imagine the tube so long that its frontal portion should 

 furnish a vapour screen absolutely opake to the radiation of its 

 hinder portion. Comparing ether vapour with olefiant gas, it 

 is, I think, evident that the radiant points of the attenuated 

 vapour which depresses the mercury column only 0*5 of an inch 

 are further apart than those of the gas which depresses the 

 column 30 inches. Consequently there is a wider door open for 

 the radiation of the distant ether particles towards the pile than 



