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Dromo's Den
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[Up] [Dromo's Den] Joseph Henry Biography HENRY, Joseph (1799-1878). An American physicist, born at Albany, N.Y., Dec. 17, 1799. He was educated at the Albany Academy, where in 1826 he became professor of mathematics and natural philosophy. Henry earned the reputation of being one of the greatest of experimenters and did more towards the development of the science of electricity than any other American. At the Albany Academy he developed the electromagnet, which had been invented a few years previously by Sturgeon of England. By insulating the wire with silk and constructing the apparatus according to certain original ideas, he obtained electromagnets of far greater power and efficiency than those of other experimenters and also transmitted the current from the battery through a considerable length of wire to the magnet. The essential feature of his apparatus was the winding of the wire on a bobbin-like thread on a spool. He wound several coils, with separate terminals, on the same bobbin. If these coils were joined in parallel, he had a "quantity magnet," with great lifting power; if they were joined in series, he had an "intensity magnet," which could be used to perform work at a great distance from the battery, provided this last was sufficiently strong. This discovery of Henry's marked an epoch in electricity. In 1831 Henry sent a current through a mile of fine copper wire and caused the armature of the electromagnet to be attracted and strike a bell, thus producing an audible signal. This is the first electromagnetic telegraph, and Henry is to be regarded as the inventor of the principle now universally applied in modern practice. In further experiments at Princeton, where Henry was appointed professor of natural philosophy in 1832, he devised an arrangement of electromagnets and batteries, where the current transmitted to a considerable distance energized a magnet and attracted an armature which opened a "local" circuit with its battery and caused a powerful electromagnet to perform work by allowing a weight to fall. This experiment contains the principle of the telegraph relay which made possible telegraphy over considerable distances. The apparatus was set up between Henry's residence and laboratory at Princeton, and the earth was used as a return conductor for the first time. Henry was also the first to employ magnetic attraction and repulsion to produce motion and constructed a simple magnetic engine which had the first automatic pole changer or commutator ever applied to the galvanic battery. Henry's greatest contribution to electricity was the discovery of the method of producing induced currents—the underlying principle of dynamos, transformers, etc. In this he anticipated Faraday by some years, although part of his work was not published for several years. He discovered the phenomena of self-induction in August, 1829, and of mutual induction in August, 1830. Later, in 1842, while at Princeton, he discovered that in the discharge of a Leyden jar the phenomenon is an oscillating one, and further that this discharge would induce discharges in other circuits at a considerable distance; in other words, he discovered the essential phenomena of wireless telegraphy. In 1846 he was chosen secretary of the Smithsonian Institution at Washington, a position that he held until his death, on May 13, 1878. In 1849 he was elected president of the American Association for the Advancement of Science, and in 1858 he was chosen president of the National Academy of Sciences, of which body he was an original member. Upon the establishment of the Lighthouse Board in 1852, Professor Henry was appointed a member and in 1871 became its head. He carried on in this capacity a number of important tests for the government which resulted in the improvement of fog signals and the various lights and lighthouses. He was also interested in meteorology, and in his reports, as secretary, he urged the government to collect and distribute meteorological information. He suggested the use of the telegraph for this purpose, and for a number of years this important work was under the direction of the Smithsonian Institution. Terrestrial magnetism was also a subject of interest to Henry, and he not only participated in investigations on his own account, but urged upon the government the importance of having such observations made. In acoustics Professor Henry also carried on important researches, his attention being directed to this subject largely through his experiments with fog signals. Henry enjoyed no small amount of European reputation, and in his trips abroad was enthusiastically received by English and continental scientists. Henry was involved in a controversy with S. F. B. Morse (q.v.) as regards the invention of the telegraph, but it is safe to state that the former is to be regarded as the originator of the principle, while Morse perfected the method for using the electromagnet for commercial purposes. Morse, in the course of his work, met difficulties which he could not overcome until his attention was called to Henry's inventions. Henry's collected writings are to be found in the Smithsonian Miscellaneous Collection, vol. xxx (Washington, 1887). In volumes xx and xxi of the same series are to be found excellent biographical and memorial notices. Consult also Dickerson, Joseph Henry and the Magnetic Telegraph (New York, 1885). The New International Encyclopaedia, Vol. XI (New York: Dodd, Mead & Co., 1920) 159-160.
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