Scientific Serials

Abstract

Poggendorff's Annalen der Physik und Chemie, No. 6, 1876,—From experiments it is here inferred by Dr. Buff, of Giessen, that the heat conductivity of hydrogen and other gases is too small to be demonstrable by the method proposed by Magnus. Hence the supposition of a conductivity similar to that of metals (if aught more is meant, than that hydrogen can, like solid and liquid bodies, transfer heat from molecule to molecule), is unwarranted. On the other hand, hydrogen has a penetrability for heat rays which comes very near that of vacuum. Dry air absorbs 50 to 60 per cent, of heat rays from a source heated to the boiling point of water. The absorptive power of moist air exceeds that of dry air by several percentages, but not nearly so much as has been supposed by some physicists. Rock salt is not perfectly diathermanous to so-called obscure heat rays. Its “heat colour” is rather like that of dry air.—Dr. H. C. Vogel describes some interesting experiments on change in pitch of tone of a moving body; they consisted in observation of the whistle of a locomotive, and the results closely agree with Doppler's theory and calculations.—M. Wiedemann's paper on the laws of passage of electricity through gases is here concluded. The experiments relate to difference of effect according as positive or negative electrode (in the discharge apparatus) is connected to earth, effect of varying length and width of tube between the electrodes, also of varying pressure and gas, the rise of temperature produced by the discharge, effect of heating electrodes, &c. The view M, Wiedemann adopts is, that in discharge, the gas molecules on the electrodes carry off electricity with them, and impart it to others against which they are driven, and these in their turn are impelled against a third set, and so on; the case being similar to that of a row of freely suspended elastic balls, one of the end ones of which is driven against its neighbour. The author further studies the unequal expansion of the positive and negative discharge, the place where the vis viva of the moved gas masses is finally transformed into heat, the dark space at the negative electrode and the stratification of the light, and points out the relation in which his results stand to those obtained by Hittorf.—The constants of dielectricity of oil of turpentine, benzol, and two varieties of petroleum, are determined by M, Silow, by the condenser method, and their square roots are shown to correspond closely to the refractive indices of the liquids, with λ = ∞ (according to Maxwell's law).—Some anomalous phenomena of the gold-leaf electroscope are pointed out by M. Beetz (they indicate a streaming out of electricity from the leaves over the glass).—We note, lastly, a paper of contributions from the Mineralogical Institute of Strasburg University, referring to glaucophane, datolith, safrol, crystalline form and optical properties of isomerous dinitro benzol, &c.