Division I
Chap. I Explanation of Terms; With Some General Remarks
If a glass tube be rubbed in the dark with a dry hand or piece of buckskin, upon applying the knuckle to it a luminous stream or spark will appear, passing from the glass to the knuckle, attended with a crackling noise: this luminous spark or stream is called electricity.8 It is produced by the friction of several other substances, and was first observed on amber.—Hence its name, from ηλεκτρον the greek term for amber. It is a fluid extremely subtle, abounding in all nature, and is one of her principal agents; which, though generally imperceptible, sometimes becomes the object of our sight and other senses.
A glass tube, having been rubbed and producing the appearances above described, is said to be excited. The hand or buckskin, by which this is effected, is called the rubber. Electrics are all substances which can be made to produce the same appearances; the most perfect are glass, amber, sealing-wax, sulphur, gum lac, rosin &c. These are also called non-conductors, from their inability to conduct the electric fluid. Conductors or non-electrics are those bodies which cannot be excited, but have the power of transmitting electricity; such are metals, water, the bodies of animals, an imperfect vacuum, heat &c. But strictly speaking, there are no perfect conductors or non-conductors.
A body is said to be in its natural state, when it is in the same state, with respect to electricity, as the mass of the earth.
When a body has more of the electric fluid than its natural quantity, it is said to be electrified positively, when less, negatively; but neither of these cases can occur in a conductor, unless the communication between it and the earth be cut off by the intervention of an electric or non-conductor. When this happens, the conductor is said to be insulated.
It may not be amiss here to mention, that the terms electric or an electric per se, and non-electric, were at first made use of from an erroneous idea that only those called electrics, contained the electric matter in their substance, which was capable of being excited by friction, and communicated by them to those called non-electrics, and supposed to be destitute of it: for glass and other electrics, being rubbed, discovered signs of having it, by snapping on the approach of a finger or other conductor, and by attracting and repelling light bodies; while other substances could not be made to produce any such effect. It has however since been proved by experiments, that both electrics and non-electrics contain this matter in their substance; but that non-electrics cannot be excited, owing to the fluid diffusing itself through them as soon as collected. These terms are therefore improper, and as the only difference is that some bodies will conduct electricity and others will not, the terms non-conductor and conductor are those which might generally be used with the most propriety in speaking on this subject; though, in conformity with custom, we shall often use non-conductor and electric as synonymous.