Joseph Henry

HENRY, JOSEPH (1i97-1878), American physicist and scientific administrator, was born in Albany, N.Y., on Dec. 17, of Scottish ancestry. Henry attended a country district school to the age of 13; showing little interest in study, he was apprenticed to a watchmaker. A popular book on natural history picked up in his 16th year awoke his ambition, so that he resumed his education, attending Albany academy, teaching in country schools and tutoring to pay his way; completing the prescribed course, he continued his studies in chemistry, anatomy and physiology with a view to practising medicine. An unexpected appointment in 1825 to survey a route for a State road from the Hudson river to Lake Erie changed his goal to engineering, and it was with some reluctance that in 1826 he accepted an appoint ment to teach mathematics and natural philosophy in the Albany academy.

But his decision proved a most happy one. Beginning experi ments in electromagnetism, Henry was the first to insulate wire for the magnetic coil; he invented the "spool" or "bobbin" wind ing; he discovered the necessary law of proportion between the electromotive force in the battery and the resistance of the mag net. He thus worked out for the first time the differing functions of two entirely different kinds of electromagnets; the one sur rounded by numerous coils of no great length revolutionized the feeble electromagnet of Sturgeon. The other surrounded by a continuous coil of very great length made possible for the first time the transmission of a current over a great distance with little loss. Every electrical dynamo or motor uses the electro magnet in practically the form in which it was left by Henry in 1829. The principles involved in the "intensity" magnet con stitute the indispensable basis of every form of the electro magnetic telegraph since invented, and Henry himself invented and demonstrated what appears to have been the first prac tical electromagnetic telegraph in 183o-31 at Albany. It con sisted of a mile of copper bell-wire interposed in a circuit between a small Cruickshanks battery and an "intensity" magnet of con tinuous fine coil. A permanent magnet pivoted to swing hori zontally like the compass needle, was arranged so that one end remained in contact with a leg of the soft iron core, while the other end was near an office bell. At each excitation of the electromagnet the suspended magnet was repelled from one leg and attracted by the other, so that its free end tapped the bell. This was the first instance of magnetizing iron at a great distance, or of a suitable combination of magnet and battery being so arranged as to be capable of such action. Reporting his achieve ments in Silliman's Jcurnal in 1831 Henry pointed out that the way was now clear for the invention of the commercial electro magnetic telegraph. In 1835, after his transfer to Princeton, he added a step in the invention of the "relay" by which a relatively feeble current operated an electromagnet which in turn controlled the local circuit of a more powerful magnet. This invention is extensively used in the field of electrical control, known as distant control. It was also in 1835 that Henry first used the earth as a return conductor. But in 1829 he had devised and constructed the first electromagnetic motor, an oscillating machine with automatic pole-changer, publishing a description of it in 1831. Tais machine was the forerunner of all electric motors. In the same period he made two other fundamental discoveries. The honour for the discovery of self-induction which he announced in 1832 has been universally conceded to him, and it was chiefly in recognition of this achievement that the International Con gress of Electricians in Chicago in 1893 gave his name to the standard unit of inductive resistance. The other discovery, that of electromagnetic induction, was made independently and at the same period by both Henry and Faraday, and since the latter published first, the credit is rightfully given to him.

Professorship at Princeton.

In 1832 Henry was appointed to fill the chair of natural philosophy at Princeton. In addition to courses in physics and mathematics he lectured in chemistry, mineralogy, geology; later adding astronomy and architecture. Continuing his physical researches, he discovered that a current of low potential could induce a current of high potential by a suitable arrangement of the coils. He elucidated the laws upon which the electrical transformer of to-day is constructed. He found, also, that a second induced current could induce a third; the third a fourth ; and so on, indefinitely ; and that these currents could be induced at a distance. Some of his experiments in induc tion involved the transmission of electric force without wires through the floors and walls of buildings, and in one case he mag netized a needle by the transmission from a lightning flash 8 m. away. This appears to be the earliest record of the action of ether waves of the type employed in radio telegraphy and tele phony to-day. The discovery of the oscillatory character of the electrical discharge came in 1842. Outside the field of electricity, Henry showed that liquids and solids generally have the same amount of cohesion. He showed, by means of a thermo-galvano meter, that sun spots radiate less heat than the general solar sur face. He invented a new method for determining the velocity of projectiles. And in 1844 be presented a theoretical paper fore shadowing the principle of the conservation of energy.

Secretaryship at Smithsonian Institution.

In Dec. 1846 the second great period of Henry's life began with his election as first secretary of the newly formed Smithsonian Institution. The plan of organization which he drew up for it was so far beyond the average intelligence of his day as to meet with bitter opposition. But scientific men turned to the institution as a rally ing and guiding centre. Under his leadership branches of science hitherto unworked in the United States were taken up; activity in all fields was tremendously stirred ; scientific exploration was made a beneficiary of the military exploration and commercial exploitation of the West; the Government's support of scientific activity was enlisted and given direction.

Creation of U.S. Weather Service.

While at Albany he had devoted much attention to meteorology, realizing the need for much more data, and one of his first acts at the Smithsonian was to organize a corps of volunteer observers spread over the conti nent. He introduced standard instruments from abroad, prepared tables of instructions, and for 3o years maintained the investiga tions, collecting, reducing and publishing results which now form a considerable portion of the foundation of meteorological science. In this connection he was the first to use the telegraph to transmit weather reports; the first to indicate daily atmos pheric conditions on a map; the first to embrace a continent under a single system; the first to make weather forecasts from the data obtained. The success of the Smithsonian meteorological work resulted in the creation of the U.S. weather bureau.

A second main achievement while at the Smithsonian was to supply American science with the first great agency for free publication of results. Of almost equal importance was the sys tem Henry inaugurated of distribution of these publications to libraries and scientific bodies throughout the world. This soon developed into the system of international exchanges by which scientific and later government publications were exchanged be tween the rest of the world and America through the Smithsonian.

Other Scientific Work.

In 1852 Henry became a member of the lighthouse board, serving as chairman from 1871 till his death. This gave him the incentive to make his classical re searches on sound in relation to fog signalling which provided his country with the most serviceable system of fog signals known to maritime powers. His researches also enabled the Government to exchange sperm oil for lard oil and later lard oil for mineral oil as an illuminant, greatly increasing the efficiency of light beacons. He directed the mobilization of scientific effort during the Civil War and was a prime mover in the organization of the National Academy of Sciences of which he was the second president. He also took a leading part in the organization of the American Association for the Advancement of Science and of the Philosophical Society of Washington.

Henry was by general consent the foremost of American physicists ; his influence, not only upon the development of scientific work in the United States, but upon its character, can not be overestimated. He was a man of varied culture, of large breadth and liberality of views, of generous impulses, of great gentleness and courtesy of manner, combined with equal firmness of purpose and energy of action. He died in Washington on May 13, 1878. (C. G. A.)