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The author of this Paper states that he procured several vacuum-tubes from M. Geissler of Bonn, and alludes to the experiments made in similarly constructed tubes by M. Plücker (Phil. Mag. August 1858), but finding it impracticable to ascertain with accuracy the nature of the residual gas, he reluctantly laid them aside. All the vacuum-tubes in which his experiments were made, were prepared by himself or in his presence; as each was exhausted and hermetically sealed, it was marked with a consecutive number; upwards of 100 were thus prepared; many were broken or otherwise destroyed, but the remainder he retains with the original numbers for future reference. The author uses several terms, which he explains: air, hydrogen, oxygen, or nitrogen (mercurial) denote that the vacuum-tube contains vapour of mercuryplus the air or gas remaining in the tube with which it was filled previous to the introduction of the mercury: he applies the terms outer positive or negative, and inner positive or negative, to denote the character of the discharge from the terminals; conductive and reciprocating denote the peculiar conditions of discharges from an induction apparatus when taken in vacuum-tubes; with a conductive discharge the needle of a galvanometer placed in the circuit will be deflected, as are also the stratifications on the approach of a magnet—they having, as the author has shown in his former communication, a tendency to rotate as a whole round either pole, but in contrary directions; in a reciprocating discharge the stratifications are confused, they are divided or separated by the magnet, and the needle of a galvanometer placed in the circuit is not deflected. The author explains the condition which the stratified discharge assumes if any air or gas remains or is subsequently introduced into a Torricellian vacuum, and describes what he denominates a white and a blue tongue discharge, which under certain conditions always appears at the negative terminal. In Torricellian vacua, if air or nitrogen is introduced, the stratifications, exclusive of their altered form, exhibit a red colour, while when hydrogen or oxygen is added, they retain the bluish-grey appearance: when the ends of the tubes were punctured by means of an electrical spark from a machine, the air or gas could be admitted so gradually as to occupy two or three hours in the experiment, and in this manner the preceding results were obtained.

II. On the stratifications in electrical discharges, as observed in torricellian and other vacua