Page:Proceedings of the Royal Society of London Vol 60.djvu/235

Rh tivity, compared with air as unity, of 01350 ; the heavier portion, of 0-1524. The ratio of these numbers is very nearly that between the densities of the gases, viz.:—

01350 0-1524 1- 876 2- 118’ instead of 1-876 2133 '

It must be remai-ked 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, assuming that the densities calculated from the diffusion-rates are correct, the densities of the two gases, supposing that two exist, are 1"871. find 2" 133, I’espectively.

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 portions, 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 recommends 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 218, 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 suggestion. 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