Electricity is a property belonging to, or capable of being communicated to, all substances whatever; and whereas by some of them it is transmitted with great ease, and by others with much difficulty, they have been divided into two classes, and denominated _conductors_ or _non-conductors_ of electricity. Also the latter receiving this power by friction, and other means, are termed _electrics_, and the former _non-electrics_. Metals of all kinds, and water, are conductors, though in very different degrees; so also is charcoal. All other substances, and also a perfect vacuum, are non-conductors of electricity. But many of these substances, when they are made very hot, as glass, resin, baked wood, and perhaps all the rest on which the experiment can be made in this state, are conductors. It is the property of all kinds of electrics, when they are rubbed by bodies different from themselves, to attract light substances of all kinds, to exhibit an appearance of _light_, attended with a particular _sound_, on the approach of any conductor; and if the nostrils are presented, they are affected with a _smell_ like that of phosphorus. This attraction is most easily explained by supposing that electricity is produced by a fluid exceedingly elastic, or repulsive of itself, and attracted by all other substances. An electric exhibiting the appearances above mentioned, is said to be _excited_, and some of them, particularly the _tourmaline_, are excited by heating and cooling, as well as by friction. It appears, however, that excitation consists in the mere transferring of electricity from one substance to another, and that the great source of electricity is in the earth. On this account it is necessary to the considerable excitation of any electric, that the substance against which it is rubbed (hence termed _the rubber_) have a communication with the earth, by means of conductors; for if the rubber be _insulated_, that is cut off from all communication with the earth by means of electrics, the friction has but little effect. When insulated bodies have been attracted by, and brought into contact with, an excited electric, they begin to be repelled by it, and also to repel one another; nor will they be attracted again till they have been brought into contact with some conductor communicating with the earth; but after this they will be attracted as at first. If conductors be _insulated_, electric powers may be communicated to them by the approach of excited electrics, or the contact of other electrified bodies. They will then attract light bodies, and give sparks, &c. like the excited electrics themselves.