158 Intelligence and Miscellaneous Articles. 



interval 72-38*5 degrees Centigrade, 



7; = 0-0000689.(l + 0-00415750 0,94 . 



The experiments were made on seven vapours, for which the mean 

 lengths of path were calculated and compared with the exponents 

 of refraction determined by Dulong. 



The remarkable relation pointed out by Director Stefan, starting 

 from the view that molecules are surrounded by an envelope of 

 aether, has been confirmed in the case of vapours also. He showed 

 in gases that higher exponents of refraction correspond to shorter 

 lengths of path. Unfortunately, the refraction-exponents for only 

 two vapours (the highest hitherto observed) were determined expe- 

 rimentally by Dulong. 



The author obtained for 



Hydrogen Z = O0000151 71=1-000158 



Air 0-0000082 1-000294 



Bisulphide of carbon . . 0-0000029 1-001500 



Ether 0-0000022 1-001530 



Director Stefan calculated from the coefficients of diffusion that the 

 mean length of path of ether-vapour is 0*0000023, and of bisul- 

 phide of carbon 0-0000032, with which values the above are in very 

 good accordance. 



Finally, for the vapours examined the proportional numbers of 

 the molecular volumes were calculated from the friction-constant, 

 according to the formula deduced by Lothar Meyer, 



(\/iVi) 3 ' 



in which m v m 2 are molecular weights, and r) v v\ 2 the friction-con- 

 stants of two gaseous bodies. If the molecular volume of hydrogen 

 v 2 be taken as unity, we obtain for the molecular volume of the va- 

 pours examined the numbers in the third column of the Table. 



Vapours. 



Composition. 



v 2 



Vy 



From friction. 



After Zopp. 



Water 



H o 



cs 2 



OHOL 



C 2 H 6 



C 3 H G 



CfiH 6 



Q 4 H l0 



4-9 

 14-0 

 18-6 

 11-3 

 16-4 

 21-2 

 21-6 



22-9 

 65-5 

 87-1 

 52-9 

 76-8 

 99-2 

 101-1 



18-8 

 62-3 

 84-9 

 62-8 

 78-2 

 99-0 

 105-8 



Bisulphide of carbon. . . 

 Chloroform 



Alcohol 



Acetone 



Benzol 



Ether 





By means of the molecular volumes v v calculated after Kopp 

 from the densities, the molecular volume of hydrogen was de- 



