IV. “By the excitation of an electric, the equilibrium of the fluid is disturbed, and one part of it is overloaded with electricity, while the other contains too little.” This position must be considered as entirely hypothetical, as the manner in which the electric fluid is collected by the excitation of glass, or any other electric substance, has not yet been satisfactorily explained. V. “Conducting bodies are permeable by the electric fluid, through the whole of their substance, and do not conduct it merely over their surface.” Take a wire of any kind of metal, and cover part of it with some electric substance, as rosin, sealing-wax, &c. then discharge a jar through it, and it will be found that it conducts as well as without the electric coating. This, says Mr. Cavallo, proves that the electric matter passes through the substance of the metal, and not over the surface. A wire, adds he, continued through a vacuum is also a convincing proof of this assertion. VI. “Positive electricity is an accumulation, or too great a quantity of the electric matter contained in a body; and negative electricity is when there is too little.” This position, like the fourth, must be considered as hypothetical—the peculiar nature of the electric fluid not admitting of experiments to prove, or to disprove it. APPENDIX. NUMBER I. _A description of the Cement used for electrical purposes._ The best cement for electrical purposes is made by melting two parts of rosin, two of bee’s-wax, and one of brick-dust, or red ochre, together. This method of making cement is much preferable to that of rosin alone, as it is not so brittle, and at the same time it insulates equally well. NUMBER II. _A Composition for Coating Cylinders or Globes._ The most approved composition for lining glass cylinders or globes, is made with four parts of Venice turpentine, one part of rosin, and one of bee’s-wax.—They must be boiled together for about two hours over a slow fire, and stirred very frequently; afterwards the composition is left to cool, when it is fit for use. If a cylinder or globe is to be lined with this mixture, a sufficient quantity must be pulverised, and introduced into the glass; then by holding the glass near the fire, the composition is melted, and by a little skill may be spread over all its internal surface, to about the thickness of a wafer.—The glass, however, must be heated very gradually, otherwise, there is danger of its breaking in the operation. NUMBER III. _To make the best kind of Amalgam for exciting Electrics.—_