248 PHENOMENA DEPENDENT ON MOLECULAR PATHS 93 



hindered by a partition. The explanation of the extreme 

 slowness of this free diffusion between gases is now the 

 special problem before us. 1 



Passing over the older observations of Dal ton, 2 

 Berthollet, 3 Graham, 4 and others, I choose, as instances, 

 the experiments carried out by Loschmidt 5 on the 

 diffusion of gases. 



A glass tube, 975 mm. long and of 26 mm. diameter, 

 which can be closed at both ends by flat glass plates and 

 glass stopcocks, was cut into two parts of equal lengths, 

 which could at will be shut off from each other or put into 

 connection by means of a slider made of a thin sheet of steel 

 in which was a hole as large as the inner section of the 

 tube. After the two halves had been filled with different 

 gases under the same pressure, the slider was opened so that 

 the gases began to mix, and after the lapse of a measured 

 time from half an hour to an hour the slider was again 

 closed, and the gas in each half of the tube was then 

 analysed in order to determine the degree to which the 

 mixing had progressed during the time of the experiment, 

 and from this to discover the speed of diffusion. 



A theory developed by Stefan 6 was employed for the 

 reduction of these experiments. This starts with the 

 assumption, made also by Maxwell 7 and Boltzmann, 8 



1 We must not conclude that, because Thos. Graham so judiciously distin- 

 guished these differing phenomena by different names, he was the first to employ 

 these names. The term diffusion was used by Da It on (' On the Tendency of 

 Elastic Fluids to Diffuse through Each Other,' Mem. Manch. Soc. 1805, new 

 series, i. p. 244) and Priestley (Trans. Amer. Phil. Soc. 1802, v. p. 15 ; 'Ex- 

 periments and Observations relating to Various Branches of Natural Philo- 

 sophy,' Birmingham 1781, iii. sect. 27, 3, p. 390. 



2 In different places ; Gilb. Ann. 1807, xxvii. p. 388. 



3 M&m. d'Arcueil, 1809, ii. p. 463. 



4 Quarterly Journ. of Sc. Lit. and Art, 1829, p. 74 ; Pogg. Ann. 1829, xvii. 

 p. 37,5. 



5 ' Experimentaluntersuchungen uber die Diffusion von Gasen ohne porose 

 Scheidewande,' Wien. Sitzungsber. Abth. 2, 1870, Ixi. p. 367 ; Ixii. p. 468 ; con- 

 tinued by Wretschko, Ixii. p. 575 ; and by Benigar, Ixii. p. 687. 



6 Wiener Sitzungsber. Abth. 2, 1871, Ixiii. p. 63 ; 1872, Ixv. p. 323. 



7 Phil. Mag. [4] 1860, xx. p. 21 ; 1868, xxxv. p. 199. Scientific Papers, i. 

 p. 392 ; ii. p. 57. 



8 ' Weitere Studien u.s.w.' Wien. Sitzungsber. Abth. 2, 1872, Ixvi. p. 324 ; 

 1878, Ixxviii. p. 733 ; 1882, Ixxxvi. p. 63 ; 1883, Ixxxviii. p. 835. 



