In this experiment, the coated part of the tube answers the double purpose of the electrical machine and Leyden phial; the uncoated part serving as a handle, to hold the instrument by. The friction on the outside accumulates a quantity of positive electricity upon it, and this electricity, in virtue of its sphere of action, forces out a quantity from the inside. Then, by taking the sparks from the knobbed wire, this inside electricity is removed, and it consequently remains under-charged, or negatively electrified; and it also follows, that the positive electricity of the outside, comes closer to the surface of the glass, and begins to form the charge. A small phial may be charged by giving the sparks from the knobbed wire of the tube to that of the phial; but the phial will be charged negatively, whereas the tube is charged positively. _To fire the electrical Cannon by inflammable Air._ This instrument consists of a metallic barrel, made in the shape of a common cannon,—a glass tube is cemented into the top of the barrel, in the place of a touch-hole, and through this tube a wire passes, which is bent so as to come within an eighth of an inch of the inner surface of the cannon,—on the outer end of this wire, a ball is fixed, which serves to receive a spark from a charged jar, or from the prime-conductor. The inflammable air with which this cannon is to be fired, may be prepared in a common porter bottle, by mixing a handful of iron filings with two wine-glassfuls of water, and an ounce of sulphuric acid, commonly called _oil of vitriol_. The air when thus made should be kept in a bottle closely stopped. To use the instrument, have ready a cork, fitted to the mouth of the cannon,—uncork the bottle containing the air, and immediately apply the cannon to the mouth of the bottle; a sufficient quantity of the gas will rise into the cannon, in the course of a few seconds, when both the cannon and bottle must be corked. Now, if the knob of the wire passing through the tube be applied to the prime-conductor, so that a spark may pass through it to the inner surface of the cannon, the gas will be inflamed with a loud report, and the cork will be forced out with considerable violence. _Curious Figures made upon Glass, Paper, and other Substances, by means of Electricity._ Professor Lichtenburg first observed some curious figures made with pulverized rosin, on a large electrophorus; but since this original discovery, a variety of other methods have been contrived, for making them upon glass, paper, resinous substances and many others. The ingenious electrician may derive considerable information from these figures; their various appearances, in many instances, showing him the direction and quality of the electric fluid.