The Homogeneity of Helium and Argon. 215 



tivity, compared with air as unity, of O1350 ; the heavier portion, of 

 0*1524. The ratio of these numbers is very nearly that between the 

 densities of the gases, viz. : 



0*1350 1-876 , 1-876 



00824 = 2018' m8tead f MM ' 



Conclusion. 



It must be remarked that the rate of diffusion of helium is too 

 rapid for its density measured by weighing. There can be no doubt, 

 we think, that the density of the lighter portion, instead of being 

 1-874, would be, if actually weighed, 2'05 or 2*08. And the heavier 

 portion has doubtless a proportionately higher density. But, assum- 

 ing that the densities calculated from the diffusion-rates are correct, 

 the densities of the two gases, supposing that two exist, are T871. 

 and 2*133, respectively. 



Also, we must not omit to state that careful experiments were made 

 with the more rapidly diffusing gas to prove that the first portions 

 passing over did not diffuse at a more rapid rate than the later por- 

 tions, no difference in diffusion rates, compared with those of hydrogen 

 under the same circumstances having been detected. 



That helium, then, consists of a mixture of two or more distinct 

 gases is one solution of the problem, probably the one which recom- 

 mends itself at first sight. But there is another, so revolutionary 

 in its character that much must be done before it can be regarded 

 as even worthy to be entertained. So much has, however, been lost 

 to science by what may be termed scientific incredulity, that we 

 regard it as well worth putting to a rigorous proof. 



It is that a separation has been effected of light molecules from 

 heavy molecules ; that, in fact, a gas in this case helium is not 

 constituted entirely of molecules of the same weight, but that the 

 mixture of molecules which we term helium have weights which 

 average 2"18, or whatever the density of ordinary undiffused helium 

 may ultimately be found to be. The same supposition would, of 

 course, be applicable to oxygen, nitrogen, or any gas. In separating 

 such molecules from each other a practical limit must necessarily be 

 reached, and this limit appears to have been reached with helium. 



There is negative and positive probability in favour of this sug- 

 gestion. First, no gas has been submitted to methodical diffusion 

 with a view to effect such a separation, argon excepted ; and here, 

 too, there is faint evidence of a similar kind. It is proposed to carry 

 out similar experiments with gases of undoubted homogeneity 

 according to the usual views ; and till such experiments have been 

 made, it is impossible to decide the point definitely. 



Second, Mr. E. C. C. Baly's experiments on oxygen appear to 



