Conductivity

The quality of being conductive. Conduct'or, n. One who conducts; a leader; a guide; a chief; a commander; a director; a manager; an overseer. - One who has charge of a public travelling carriage, as a car, or train of cars, on a railroad or trolley line. Something that conducts or guides; as a lightning-conductor. (Mus.) The person placed at the head of a band of musicians to lead the performance and beat the time. In Germany, the term Dirigent is used, which is more expre ive. The French name is chief of the orchestra (Chef d' Orchestre). (Elect.) C. and non-C. of electricity are terms applied to substances according to whether they receive and communicate electricity, or not. When a rod of metal is made to touch the prime C. of an electric machine after it has been charged, all the electricity pa es through the rod, and through the body of the experimenter into the ground. The metal in this case is said to be a conductor . If, however, a rod composed of gla or shell-lac is used, the electricity will not be carried off. In this case the gla or shell-lac is said to be a non - conductor . All substances conduct electricity in the same manner from metals to lac and gases, but in different degrees; and the term non-conductor only signifies that the substance has a very low power of conducting. In frictional electricity, the best conductors are the metals; after which come graphite, seawater, spring-water, and rain-water. Ice is a worse C. than fluid water. Alcohol, ether, paper, dry wood, and straw are also inferior conductors. Among the substances reckoned as non-conductors are shell-lac, amber, resin, sulphur, gla , silk, wool, hair, feathers, . In galvanic electricity the substances that are found to conduct frictional electricity in a feeble manner are almost, if not altogether, non-conductors; and the metals which are nearly alike in conveying frictional electricity differ widely in their powers of conveying that obtained from the galvanic battery. When heated, the conducting power of metals is weakened; but in nearly all other substances the effect of heat is to increase the power of conduction. Shell-lac, wax, amber, and sulphur become conductors when fused; and gla conducts readily at a red heat. A C. is said to be insulated when it rests upon non-conducting supports. In electrical apparatus gla is the non-conductor most employed. It requires to be kept very dry, as any moisture on its surface weakens its insulating power. The discovery of the identity of lightning and electricity has not been without its practical results; amongst which may be reckoned the application of lightning - conductors to buildings and ships. For buildings, Franklin's original proposition is that generally adopted. It consists in erecting a continuous metallic rod by the side of any building. The rod is pointed at each end, and extended above the highest part of the place to be protected at one extremity, the other penetrating deep into the earth, or in contact with water. The highest point of the rod is generally made of copper, which does not rust. Iron points are very liable to acquire a coating of rust, which is a non-conductor, and diminishes their efficacy.