ELECTRICITY, Few sciences can claim as great an antiquity as that of electricity. It is believed that Thales of Miletus (c.640-546 u.e.) knew that amber. after being rubbed. acquired the property of attracting bodies: and Theophrastus (e.372-2S7 n.c.). in his treatise On (1(i/is. mentions the fact that this power is not peculiar to amber. No definite scientific in formation was acquired. however, until the close of the sixteenth century. William Gilbert (q.v.) published in 1600 his great work lr Magnet,. In this book he used for the first time the terms 'electric forty' and 'electric attraction; and dis tinguished between 'electric.' and lion ries•— the former name being given to bodies which act as amber duos when 1.111)1)0(1. the latter to bodies. such as met(ils, which, when held in the hand and rubbed, do not acquire the power of attraction. Ile elearly distinguished between magnetic and electric action. as Cardan (1501-76) had also done hefore, but in an imperfect manner. Robert Boyle. Sir Isaac Newton. and others made many interesting observations on electrical phenomena. the former showing that electric attraction takes platy through a vacuum. Otto VOD Guerieke, the inventor of a rude form of electrical machine (q.v.), also disco•ered electric• induction, the phenomena of which were studied with special care by Canton nearly a eentury later. Hawks bee made several important advances, being the first to show how to electrify metals by nabbing, and also the first to observe that electric. charges are only on the surfaces of metals, not in the in terior.
During the eighteenth century electric phe nomena were studied very extensively, especially toward its close. when means of producing elec tric currents were discovered. Stephen Gray (i.v.), in the early part of the century, observed the important fact that electric forces could be carried for a considerable distance by means of pack-thread and other bodies. thus discovering electric conduction, and he was then led to dis tinguish between conductors and non-conductors. The possibility of two kinds of electricity—vitre ous and resinous, or positive and negative— MA, established independently by du Fay in France and Kinne•sley in Philadelphia. The former developed also a two-fluid theory of elec tricity which persisted for many The Leyden jar was discovered by accident in 1745, and from this time on public exhibitions of elec tric phenomena were most popular. Most inter esting and important work was being done also in America by Benjamin Franklin (q.v.) and a
group of his friends. lie proposed a one-tluid theory, which, after more than a century of neglect, has reappeared as a possible explanation of the new phenomena concerning 'corpuscles' and ions. Having noticed the effect of points on mndnetors in btalies, and believing that lightning is an electric phenomenon. Frank lin, in 1750, proposed an experiment to test his theory. It was to extent! a long. pointed wire upward from a steeple. and to see if electrical charges could be observed at the lower end of the wire when a thunder-cloud passed overhead. The actual experiment was carried out according to these directions in 1752. in France. by Dalibard. and later by Delon and in the same year Frank lin performed his kite experiment. Soon after this which had been sug gested by Franklin. bevame popular both in America and Europe. The main phenomena of pyro-electricity were discovered by „Epinus, Berg man. and Canton. about 1770. Many of the most important in electricity which were made known durinthe nineteenth century by Coulomb. (dun. and Fa raday. were in reality discovered by Henry Cavendish (175I-181))), one of the world's greatest philosophers. He showed that the capa•ity of a condenser varied with its size and with the non-conductor used: he studied the conducting power of solutions: and he also dis covered what is now- called law. saw. further, from mathematical considerations. that if electrical charges act on each other with a foree varying directly as the amounts of the eharges and inversely as the square of their dis tan•e apart. then a eharged conductor must have its charge entirely on its surface: whereas, if the law of action were different. there would be sonic charge 011 the interior. By a most in genious experiment, performed before 1775. he showed tl at. to the limit of accuracy of his ap there was :111;0111telY 110 charge on the interior. These electrical papers of Cavendish were not published until 1879, when they were edited by clerk Maxwell. The law of electric act it n was proved indept ndently and in a ac curate manner by C01001111, fq v.1. in Many improvements in electrical apparatn.". were made: a circular glass plate and a rubber mated with a tin amalgam were sub stituted for the sulphur globe and the hand as used by von Guericke. The gold-leaf electro scope was invented in 1781i, by Abreiliam Bennet. and was improved by Volta (q.v.). The latter also. in 1775, invented the electrophorus.