If a thin bottle be exhausted of air by means of an air pump, it will receive a considerable charge of electricity, by applying its bottom to an electrified prime conductor. In performing this experiment the bottle is to be held by the neck or near the mouth, and the electric matter will pass through the vacuum, and along the inner surface of the bottle, to the hand, from that end of it which is nearest to the prime conductor. The luminous appearance exhibited by this experiment is exceedingly beautiful in the dark, especially if the bottle be of any considerable length. It exactly resembles those lights which appear in the northern sky, and which are called streamers or the aurora borealis. If one hand be applied to the part of the bottle which was before presented to the prime conductor, while the other remains at the neck, a shock will be felt, at which instant the natural state of the inner surface is restored by a flash, which is seen pervading the vacuum between the two hands.—The principle on which this experiment depends will be explained hereafter. CHAP. XI. _A description of the electrophorus, and some of its phenomena accounted for._ The electrophorus is a machine, consisting of two plates, usually of a circular form. At first the under plate was of glass covered with sealing wax; but there is little occasion to be particular, with regard, either to the substance of the lower plate, or to the electric with which it is covered; a metallic plate however is preferable to a wooden one, though the latter will answer very well. This plate must be covered with an electric: pure sulphur answers nearly as well as the dearer electrics gum lac, sealing wax &c. The upper plate is made of brass, or a piece of paste-board covered with tin foil or silvered paper, which must be nearly of the same dimensions as the electric plate: this plate must be furnished with an electric handle, which, by means of a metallic or wooden socket is fastened to its centre. This instrument was invented by Mr. Volta, an Italian philosopher. The manner of using it is as follows.