THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



FEBRUARY 1859. 



X. On the Mean Length of the Paths described by the separate 

 Molecules of Gaseous Bodies on the occurrence of Molecular 

 Motion : together with some other Remarks upon the Mechanical 

 Theory of Heat. By R. Clausius*. 



(1.) rpiHE February Number of PoggeudorfF's Annalen con- 

 JL tains a paper by Buijs-Ballot " On the Nature of 

 the Motion which we call Heat and Electricity." Amongst the 

 objections which the author there makes against the views ad- 

 vanced by Joule, Kronig, and myself concerning the molecular 

 motion of gaseous bodies, the following deserves especial con- 

 sideration. Attention is drawn to the circumstance that, if the 

 molecules moved in straight lines, volumes of gases in contact 

 would necessarily speedily mix with one another, — a result which 

 does not actually take place. To prove that such mixture does 

 not occur, the following facts are adduced (p. 250) : — " How 

 then does it happen that tobacco-smoke, in rooms, remains so 

 long extended in immoveable layers ? " Mention is also made 

 of the same appearance with clouds of smoke in the open air. 

 Further, " If sulphuretted hydrogen or chlorine be evolved in 

 one corner of a room, entire minutes elapse before they are 

 smelt in another corner, although the particles of gas must have 

 had to traverse the room hundreds of times in a second." 

 Further, " How could carbonic acid gas remain so long in an 

 open vessel ? " 



These objections may, at first glance, appear to have very great 

 weight ; and I consider it therefore necessary to prove, by sjiecial 

 considerations, that the facts adduced arc perfectly rcconcilcablc 

 with the tlicory of the rectilineal motion of the molecules. In- 

 deed, I rejoice at the discussion of this jioint by M. Buijs- 



* Translated by Dr. F. Guthrii", from Poggcmlorir's Annalen, No. 10, 

 185R. 



Phil. Mag. S. 4. Vol. 17. No. 1 13. Feb. 1859. G 



