Third. Those which exhibit electric appearances for any length of time, and which communicate to conducting bodies, the greatest electric power.—Of these, the substances called negative electrics, such as sealing-wax, resinous substances, and resinous compounds, are the best.
Fourth. Those which readily exhibit electrical phenomena by heating and cooling.—Of these, the tourmaline[[9]] is the principal.
The best method of disturbing the electric fluid, that is of making it pass from one body to another, is friction. This may be done either by rubbing one electric with another, or with a conductor; but the electricity is generally stronger in the latter case. Other methods for causing electrics to shew electric appearances, are, melting, or pouring a melted electric on another substance, heating and cooling, evaporating or effervescing.
CHAP. III.
Of Electrics and Conductors.
All bodies in nature are, with reference to this subject, divided into two classes, electrics and conductors.
It has been fully demonstrated by experiment, that no substance which is a conductor can be excited so as to exhibit electrical phenomena: and in the same manner it has been found, that no substance which can be excited, is a conductor. But as we have already hinted, there is, strictly speaking, no substance which is a perfect conductor or non-conductor; because, on the one hand, the electric fluid meets with some resistance in its passage through the best conductors; and on the other, it is in part transmitted through, or passes over the surface of, most if not all electrics.
The two following lists contain as complete an enumeration of electrics and conductors as the present state of knowledge, in regard to electricity, permits us to make.
The substances are disposed in the order of their perfection; that is, the best conductors and the best electrics are placed at the head of their respective lists, and those of an inferior kind follow, somewhat in the manner of a scale graduated downward. Perfect exactness however is not to be here expected, because the subject forbids it, and some of the specified articles are of classes of substances among which there may be a sensible difference.
Conductors or non-electrics.
Gold,