First to discover that electric charges are of two kinds--Cisternay du Fay, France, 1698-1739; Du Fay was also the first to attempt an explanation of electrical action. He supposed that electricity consists of two fluids which are separated by friction, and which neutralize each other when they combine. This theory was more fully set forth by Robert Symmer. Leyden jar--Discovered first by Von Kleist in 1745. The same discovery was made and the Leyden jar brought to the attention of the public in 1746 by Pieter van Musschenbroek in Holland. Lightning-rod--Benjamin Franklin, 1732. Electroplating--Luigi Brugnatelli, Italy, 1805. Voltaic arc, a powerful arc light produced with a battery current--Sir Humphry Davy, England, 1808. Storage battery--Ritter, Germany, 1803. Platinum wires were dipped in water and a battery current passed through. Hydrogen collected on one wire and oxygen on the other. If the platinum wires were disconnected from the battery and connected with each other by a conductor, the two wires acted like the plates of a battery, and a current would flow for a short time in the new circuit. Electromagnetism discovered--H. C. Oersted, Denmark, 1819. Galvanometer, a coil of wire around a magnetic needle for measuring the strength of an electric current--Schweigger, Germany, 1820. Motion of magnet produced by an electric current--M. Faraday, England, 1821. Thermo-electricity, an electric current produced by heating the junction of two unlike metals--Discovered by Professor Seebeck England, 1821. Principles of electrodynamics, motion produced by an electric current--Ampère, France. Announced in 1823. Law of electric circuits, Ohm's law, current strength equals electromotive force divided by resistance of the circuit--George S. Ohm, Germany. Proven by experiment in 1826; mathematical proof published in 1827. Magneto-electric induction, induction of electric currents by means of a magnetic field--M. Faraday, England, 1831. Electric telegraph--Prof. S. F. B. Morse, United States, 1832. First telegram sent in 1844--Morse. Constant electric battery--J. P. Daniell, England, 1836. First electric motor-boat--Jacobi, Russia, 1839. Induction-coil--Rhumkorff, Germany, 1851. Duplex telegraph, first practical system--Stearns, United States, about 1855-1860. Storage battery, lead plates in sulphuric acid--Gaston Planté, France, 1859. Telephone, make-and-break system, first electrical transmission of speech--Philip Reiss, Germany, 1860. Atlantic cable laid--Cyrus W. Field, 1866. Dynamo, armature coil rotates in the field of an electromagnet, armature supplies current for the electromagnet as well as for the external circuit--William Siemens, Germany, 1866.