ELECTRICITY 492 ELECTRICITY place, emitted faint flashes of light, and shortly afterward it was noticed that a similar phenomenon occurred at the sur- face of the mercury when the barometer was shaken — a fact which one of the celebrated mathematicians, Bernouilli, attempted to explain on the Cartesian system, but which was afterward cor- rectly attributed by Hawkesbee to elec- tric charges. Wall, in 1708, observed the sparks produced from amber, and Hawkesbee noticed the sparks and "snap- ping" under various modifications. Dufay and Abbe Nollet were the first to draw sparks from the human body, an experiment which attracted great atten- tion, and became a species of fashionable diversion at the time. The discovery of the Leyden jar is at- tributed to Cunaeus of Leyden, in 1746, who, while handling a vessel containing water in communication with an elec- trical machine, was surprised at receiv- ing a severe shock. A similar event had happened the year previous to Von Kleinst, a German prelate. In the 18th century the names of the principal contributors to the advance- ment of electrical science are Nevsrton, Hawkesbee, Dufay, Guericke, Cunaeus of Leyden (to whom we owe the Leyden jar), and Franklin, who, 1747, pointed out the circumstances on which the action of the Leyden jar depends. Monnier the younger discovered that the electricity which bodies can receive depends on their surface rather than their mass, and Franklin soon found that "the whole force of the bottle and power of giving a shock is in the glass itself"; he further, in 1750, suggested that electricity and lightning were identical in their nature, and in 1752 demonstrated this fact by means of his kite and key. About the same time D'Alibard and others in France erected a pointed rod 40 feet high at Marli, for the purpose of verifying Franklin's theory, which was found to give sparks on the passage of a thunder cloud. Similar experiments were re- peated throughout Europe, and in 1753 Richman was instantly killed at St. Petersburg by a discharge from a rod of this kind. The more important discoveries since those days relate rather to electricity produced by voltaic or magnetic action. In the later history of electricity no name is greater than that of Michael Faraday, who was born in London in 1794, was appointed by Sir Humphry Davy assistant in the laboratory of the Royal Institution in March, 1813, and in 1831 commenced the publication of a series of splendid discoveries in elec- tricity. The past history of electricity centers round the frictional machine and the vol- taic battery. The first-named is now only of experimental interest, and the second, if we except its use in signaling (telegraphy and telephony) , is quickly being supplanted by the more economical and vastly more powerful dynamo- machine. To this contrivance, in its ' various forms, as designed by different : makers, and in less degree to the second- ary battery (now quite in its infancy), . electricians look for the advancement of their science. The fact that the Gramme and similar machines are reversible is considered to be one of the most im- portant discoveries of the century. By reversible is meant its power to act as a motor when coupled up with a distant machine, under which circumstances its armature rapidly revolves in the reverse direction to what it would do if used directly — as in the production of the elec- tric light. By such means the electrical transmission of power from place to place has become possible. Important advances in the knowledge of the connection between electricity and matter have in recent years been made through the observation of the ionization of gases. The principal researches along this line were made by Professor J. J. Thomson, at the Cavendish Laboratory, at Cambridge, England. All gases can be made conductors of electricity when the molecules of the gas have been broken into parts, that is, ion- ized. Among the methods for ionizing gas are (1) application of high temper- ature; (2) the passage of a spark in the neighborhood; (3) exposure to Rontgen rays or to rays from a radioactive sub- stance such as uranium; (4) exposure to "cathod" rays; (5) exposure to "ultra- violet" light. It has been established that the negative ions of all gases, how- ever they may be produced, are identical. The practical application of electricity to industry and to domestic uses has been one of the great developments of the last generation. The development of the automobile has called for storage batteries of high power and electricity and has also been employed as a motor power for motor vehicles. See Motor Vehicle. In transportation, the use of electricity has come to be common, espec- ially in suburban lines of railroad whei"© a long haul is not required. For domes- tic use electricity is employed not only for lighting and heating but for devices in- cluding vacuum cleaners, electric irons, washing machines, and counties? other devices. For a discussion of the different phases of electricity and its use, see Storage Batteries, Electrical Machine, Trans- mission OF Electric Power, Dynamo,
