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HENRY, JOSEPH (1797-1878)

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Originally appearing in Volume V13, Page 300 of the 1911 Encyclopedia Britannica.
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HENRY, See also:JOSEPH (1797-1878) , See also:American physicist, was See also:born in See also:Albany, N.Y., on the 17th of See also:December 1797. He received his See also:education at an See also:ordinary school, and afterwards at the Albany See also:Academy, which enjoyed considerable reputation for the thoroughness of its classical and mathematical courses. On See also:finishing his See also:academic studies he contemplated adopting the medical profession, and prosecuted his studies in See also:chemistry, See also:anatomy and See also:physiology with that view. He occasionally contributed papers to the Albany See also:Institute, in the years 1824 and 1825, on chemical and See also:mechanical subjects; and in the latter See also:year, having been unexpectedly appointed assistant engineer on the survey of a route for a See also:state road from the See also:Hudson See also:river to See also:Lake See also:Erie, a distance somewhat over 300 m., he at once embarked with zeal and success in the new enterprise. This diversion from his See also:original See also:bent gave him an inclination to the career of See also:civil and mechanical See also:engineering; and in the See also:spring of 1826 he was elected by the trustees of the Albany Academy to the See also:chair of See also:mathematics and natural See also:philosophy in that institution. In the latter See also:part of 1827 he read before the Albany Institute his first important contribution," On Some Modifications of the Electro-Magnetic Apparatus." Struck with the See also:great improvements then recently introduced into such apparatus by See also:William See also:Sturgeon of See also:Woolwich, he had still further extended their efficiency, with considerable reduction of See also:battery-See also:power, by adopting in all the experimental circuits (where applicable) the principle of J. S. C. Schweigger's " multiplier," that is, by substituting for single See also:wire circuits, voluminous coils (Trans. Albany Institute, 1827, 1, p. 22). In See also:June 1828 and in See also:March 1829 he exhibited before the institute small electromagnets closely and repeatedly See also:wound with See also:silk-covered wire, which had a far greater lifting power than any then known.

Henry appears to have been the first to adopt insulated or silk-covered wire for the magnetic coil; and also the first to employ what may be called the " spool " winding for the limbs of the magnet. He was also the first to demonstrate experimentally the difference of See also:

action between what he called a " quantity " magnet excited by a " quantity " battery of a single pair, and an " intensity " magnet with See also:long See also:fine wire coil excited by an " intensity " battery of many elements, having their resistances suitably proportioned. He painted out that the latter See also:form alone was applicable to telegraphic purposes. A detailed See also:account of these experiments and exhibitions was not, however, published till 1831 (See also:Sill. Journ., 19, p. 400). Henry's " quantity " magnets acquired considerable celebrity at the See also:time, from their uneprecedented attractive power—one (See also:August 183o) lifting 750 lb, another (March 1831) 2300, and a third (1834) 3500. See also:Early in 1831 he arranged a small See also:office-See also:bell to be tapped by the polarized See also:armature of an " intensity " magnet, whose coil was in continuation of a mile of insulated See also:copper wire, suspended about one of the rooms of his academy. This was the first instance of magnetizing See also:iron at a distance, or of a suitable See also:combination of magnet and battery being so arranged as to be capable of such action. It was, therefore, the earliest example of a true " magnetic " See also:telegraph, all preceding experiments to this end having been on the See also:galvanometer or See also:needle principle. About the same time he devised and constructed the first electromagnetic See also:engine with automatic polechanger (Sill. Journ., 1831, 20, p.

340; and Sturgeon's See also:

Annals Electr., 1839, 3, p. 554). Early in 1832 he discovered the See also:induction of a current on itself, in a long helical wire, giving greatly increased intensity of See also:discharge (Sill. Journ., 1832, 22, p. 408). In 1832 he was elected to the chair of natural philosophy in the New See also:Jersey See also:college at See also:Princeton. In 1834 he continued and extended his researches " On the See also:Influence of a See also:Spiral Conductor in increasing the Intensity of See also:Electricity from a Galvanic Arrangement of a Single Pair," a memoir of which was read before the American Philosophical Society on the 5th of See also:February 1835. In 1835 he combined the See also:short See also:circuit of his See also:monster magnet (of 1834) with the small " intensity " magnet of an experimental telegraph wire, thereby establishing the fact that very powerful mechanical effects could be produced at a great distance by the agency of a very feeble magnet used as a circuit maker and breaker, or as a " trigger "—the precursor of later forms of relay and receiving magnets. In 1837 he paid his first visit to See also:England and See also:Europe. In 1838 he made important investigations in regard to the conditions and range of induction from See also:electrical currents—showing that induced currents, although merely momentary, produce still other or See also:tertiary currents, and thus on through successive orders of induction, with alternating signs, and with reversed initial and terminal signs. He also discovered similar successive orders of induction in the See also:case of the passage of frictional electricity (Trans. Am: Phil.

See also:

Soc., 6, pp. 303-337). Among many See also:minor observations, he discovered in 1842 the oscillatory nature of the electrical discharge, magnetizing about a thousand needles in the course of his experiments (Proc. Am. Phil. Soc., 1, p. 301). He traced the influence of induction to surprising distances, magnetizing needles in the See also:lower See also:story of a See also:house through several intervening floors by means of electrical discharges in the upper story, and also by the secondary current in a wire 220 ft. distant from the wire of the See also:primary circuit. The five See also:numbers of his Contributions to Electricity and See also:Magnetism (1835–1842) were separately republished from the Transactions. In 1843 he made some interesting original observations on "See also:Phosphorescence" (Prot. Am. Phil.Soc.,3, pp.38-44).

In 1844, by experiments on the tenacity of See also:

soap-bubbles, he showed that the molecular cohesion of See also:water is equal (if not See also:superior) to that of See also:ice, and hence, generally, that solids and their liquids have practically the same amount of cohesion (Prot. Am. Phil. Soc., 4, pp. 56 and 84). In 1845 he showed, by means of a thermo-galvanometer, that the See also:solar spots radiate less See also:heat than the See also:general solar See also:surface (Proc. Am. Phil. Soc., 4, pp. 173-176). In December 1846 Henry was elected secretary and director of the Smithsonian Institution, then just established. While closely occupied with the exacting duties of that office, he still found time to prosecute many original inquiries—as into the application of See also:acoustics to public buildings, and the best construction and arrangement of lecture-rooms, into the strength of various See also:building materials, &c.

Having early devoted much See also:

attention to See also:meteorology; both in observing and in reducing, and discussing observations, he (among his first administrative acts) organized a large and widespread See also:corps of observers, and made arrangements for simultaneous reports by means of the electric telegraph, which was yet in its See also:infancy (See also:Smithson. See also:Report for 1847, pp. 146, 147). He was the first to apply the telegraph to meteorological See also:research, to have the atmospheric conditions daily indicated on a large See also:map, to utilize the generalizations made in See also:weather forecasts, and to embrace a See also:continent under a single See also:system—See also:British See also:America and See also:Mexico being included in the See also:field of observation. In 1852, on the reorganization of the American lighthouse system, he was appointed a member of the new See also:board; and in 1871 he became the presiding officer of the See also:establishment—a position he continued to hold during the See also:rest of his See also:life. His diligent investigations into the efficiency of various illuminants in differing circumstances, and into the best conditions for developing their several maximum See also:powers of brilliancy, while greatly improving the usefulness of the See also:line of beacons along theextensive See also:coast of the See also:United States, effected at the same time a great See also:economy of See also:administration. His equally careful experiments on various acoustic See also:instruments also resulted in giving to his See also:country the most serviceable system of See also:fog-signals known to maritime powers. In the course of these varied and prolonged researches from 1865 to 1877, he also made important contributions to the See also:science of acoustics; and he established by several See also:series of laborious observations, extending over many years and along a wide coast range, the correctness of G. G. See also:Stokes's See also:hypothesis (Report Brit. Assoc., 1857, part ii. 27) that the See also:wind exerts a very marked influence in refracting See also:sound-beams.

From 1868 Henry continued to be annually chosen as See also:

president of the See also:National Academy of Sciences; and he was also president of the Philosophical Society of See also:Washington from the date of its organization in 1871. Henry was by general concession the foremost of American physicists. He was a See also:man of varied culture, of large breadth and liberality of views, of generous impulses, of great gentleness and See also:courtesy of manner, combined with equal firmness of purpose and See also:energy of action. He died at Washington on the 13th of May 1878. (S. F.

End of Article: HENRY, JOSEPH (1797-1878)

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