DISCOVERY BY MEANS OF NEW EXPERIMENTS. 537 



ductor or the direction of the current, the position and 

 direction of the magnet changed with it, so as to maintain 

 constant the foregoing relation. By means of experiments 

 with the battery current, Ampere also, previous to Sep- 

 tember 25, 1820, discovered the mutual attraction and 

 repulsion of currents in wires, and the attraction of iron 

 filings by the conducting wire, and that a spiral of wire 

 was the best for magnetising needles. He also discovered, 

 by means of experiments made daring the same year, the 

 laws of electro-magnetic attraction and repulsion of con- 

 ducting wires. Faraday, by repeating, in 1821, Ampere's 

 experiments on this subject, and studying the phenomena, 

 concluded that a magnet and an electric wire conveying 

 a current might be made to mutually revolve round each 

 other, and, by making experiments, he finally succeeded in 

 obtaining those effects, and in causing an electric wire to 

 rotate by terrestrial magnetism. 



In the year 1820, Sir William Snow Harris had strips 

 of sheet c6pper fixed from the top of the masts of a ship to 

 the copper sheathing on the bottom of the vessel, and thus 

 discovered that ships might be protected from lightning. 

 Boisgeraud, in October of the same year, proposed to discover 

 the degrees of electric-conduction resistance of bodies by 

 means of experiments with a voltaic current and Ampere's 

 galvanometer. By means of experiments with an electric 

 current, Arago, in September 1820, magnetised a steel 

 needle permanently. Seebeck, in 1822, succeeded in dis- 

 covering thermo-electricity, by attaching two wires of dif- 

 ferent metals to a galvanometer, joining their ends, and 

 heating the junction. Oersted having discovered electro- 

 magnetism in 1819, Ampere, in 1830, suggested the experi- 

 ment of an electro-magnetic telegraph ; and Wheatstone 

 and Cooke, also Morse, an American, and Steiuheil of 

 Munich, devised similar experiments, about the year 1837, 



