EPITOME OF ELECTRICITY. (continued 3)

The case is equally clear with regard to the atmosphere. The extract from Mr. Cavallo’s journal, given in the chapter upon atmospheric electricity, is a sufficient proof that the atmosphere is full of electric matter.

II. “Glass, and other electric substances, though they contain a great deal of electric matter, are nevertheless impermeable by it.” The principal arguments for the impermeability of glass by the electric fluid are drawn from the phenomena of the Leyden phial. It is very plain that there is, in charging this phial, an expulsion of fire from the outside, at the same time that it is thrown upon the inside. This appears from numberless experiments, but is most readily observable in the following. Let a coated phial be set upon an insulating stand, and the knob of another phial brought near its coating. As soon as sparks are discharged from the prime-conductor to the knob of the first, an equal number will be observed to proceed from its coating to the knob of the second. This is very remarkable, and an unphilosophical observer will scarce ever fail to conclude, that the fire runs directly through the substance of the glass. Dr. Franklin however concludes that it does not, because there is a very great accumulation of electricity on the inside of the glass, which discovers itself by a violent flash and explosion, when a communication is made between the outside and inside coatings. But it must be confessed, there is here no other 122reason for concluding the glass to be impermeable, than the probability that the electric matter is accumulated on one side of the glass and deficient on the other.

Another argument against the permeability of glass and other electrics is, that coated phials can receive but a very slight charge when their outside coating is insulated, and this can be effected only with a very powerful machine.

III. “The electric fluid violently repels itself, and attracts all other matter.” The proofs of this position have been so abundantly given in the course of this work, particularly in the chapter on electric attraction and repulsion, that we think it entirely superfluous to repeat them here.

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.

123VI. “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.

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