Tested by the appearance of the electrical discharge from the Ruhmkorff inductive coil, found by Mr. Gassiot in these researches to be the most delicate of all tests of the presence of ponderable matter, these vacuum-tubes were at length ascertained to be void even of the slightest trace of air or gas. mercurial vapour alone remaining. But the progress of the investigation required that this also should be removed, and a still nearer approach to empty space obtained. This was effected by a refined modification of Dr. Andrews's process already described, suggested by Dr. Franklaud ; tubes, into which caustic potash bad been introduced, being repeatedly filled with carbonic acid and exhausted ; finally exhausted to the utmost limit of the capability of the air-pump, and sealed. These were found, on the application of the electrical test, to be far more perfect vacua than the Torricellian, and when the infinitesimally rare included atmosphere of carbonic acid gas was exposed to the action of a large surface of hydrate of potash, the vacuum no longer permitted tho electrical discharge to pass, a result first obtained by Mr. Gassiot, and in these researches ; when the potash was heated, more ponderable matter being diffused in the tube, the discharge again passed ; but on allowing it to cool, the tube resumed its insulating state. These results were given by a tube 40 inches long and 14 inch internal diameter. An excellent carbonic-acid vacuum was obtained by the same method in an egg-shaped vessel, 22 inches long and 7 inches is its greatest diameter ; but this did not insulate the discharge,—judging from the appearance of which, this vacuum may be inferred to be about equal, though in so large a vessel, to the best Torricellian vacuum in com paratively narrow tubes. The minute fraction of ponderable matter pre sent does not appear to have been calculated in any of these instances. This is the nearest approach to a true physical vacuum that science has yet succeeded in producing. Mr. Gassiot concludes his paper with the remark—adopting a suggestion made by Mr. Brayley—" The fact that a vacuum so perfect can be obtained in a closed vessel containing such a substance as hydrate of potassa, would excite a hope that the limit to vaporation (vaporisation), the existence of which Faraday and others have, if not proved, at least rendered so probable, may be determined, and even its consequences exhibited by direct experiment." (' Phil. Trans.,' 1858, p. 157.) Such is the present condition of this 'subject, ono of the most in teresting and most extensive in its philosophical applications which can claim the attention of the physicist and the chemist. The bearings
of Mr. Gassiot's results, and of those obtained by other experimenters with similar apparatus, on the nature and theory of electricity. how ever important, are foreign to the object of this article. But the terms in which they have been described and the reasoning which has been founded upon them, involve a subject which is strictly within its scope. We conceive that the true and immediate induction from these results, is, in general terms, that in consequence of the diminu tion in density of the media through which the electricity has to pass —that is, of the diminution of the quantity of matter contained in a given space—certain properties of electricity are exhibited in a manner which a denser medium precludes it from manifesting : that this takes place up to a certain point of rarefaction, through which, if electricity can pass at all, greater intensity is required ; or it may even be that a vacuum absolutely free from ponderable matter, which luminous electricity requires for its production and convection, has been tempo rarily obtained. Considering the nature and circumstances of the vessels and materials by which only it can be obtained, it must necessa rily be temporary only. But the results have been described and reasoned from ,(originally, we believe, on account of certain views respecting the nature of matter entertained by Mr. Grove, to which we have elsewhere adverted), as if they depended, not on the removal of ponderable matter, but on its presence in an increased degree and with increased causation of phenomena, But in proportion to the com pleteness with which such matter is removed from an inclosed space, the ether which it still contains will be more free to exhibit its pecu liar properties, unimpaired by the presence of an inferior and grosser form of matter ; and the phenomena which have been attributed to "attenuated (ordinary) matter," ought, we conceive, to be ascribed to the unincumbered ether which remains. The fact, that a certain amount of ordinary matter is essential to the manifestation of any sensible effects whatever by the electricity does not militate against this conclusion. It should be so. The conduction, or the convection by induction, of electricity belongs to ordinary matter, while the reception and transmission of impressions from it in the form of light and heat,•belong to the higher order of matter, the ether.