Professor Henry And His Philosophical Toys


The experiment Henry cited in his paper was considerably more sophisticated than any Faraday had announced. The result was the same: electricity from magnetism, or “mutual” induction, as it was called. Moreover, toward the end of his paper Henry modestly recorded one brand-new discovery: “I may however, mention one fact which I have not seen noticed in any work.” That “fact” was self-induction, or “extra” current, as it was referred to. Self-induction, first observed as a spark upon the breaking of a long circuit, was the key to multiplex telegraphy and many other systems of the coming electrical age. This tag-end mention of self-induction was a fortunate afterthought on Henry’s part. In 1834 Faraday announced that he had discovered self-induction, assuming it to be an original finding.

Nobody knows the exact date of Henry’s crucial experiment on mutual induction. Mary Henry, his daughter and biographer, claims it may have been in 1829, but other biographers believe August of 1830 to be a more likely date. Many consider the argument academic in view of the fact that Faraday was first by prior publication. Nevertheless, Henry’s paper put Albany on the scientific map with London, and Faraday himself acknowledged the new American learning several years later in London. When Henry, who was travelling abroad, showed him the best way to rig an experiment in self-induction, Faraday is said to have cried out, “Hurrah for the Yankee experiment.”

In 1832, after six years at the Albany Academy, Henry accepted the chair of natural philosophy at Princeton, then the College of New Jersey. There Henry was involved in investigations of natural phenomena so far ahead of his time, and he was making such consistent progress, that it is tempting to speculate on what scientific wonders he might have discovered had his researches not been interrupted.

All the same, what he did discover was impressive enough. Several of his experiments indicated that electromagnetic waves and light waves were similar—a finding of enormous significance to science which was not finally proved until 1900. (Guglielmo Marconi later paid tribute to this work. After successfully transmitting a radio signal across the Atlantic in 1902, he acknowledged his debt to Clerk Maxwell, Lord Kelvin, Heinrich Hertz—and Joseph Henry.) In his study of the sun as a source of energy Henry came very close to another great discovery. “If he had published,” wrote Asa Gray, the great American botanist, “Henry’s name would have been prominent among the pioneers … of the modern doctrine of the conservation of energy.”

At Princeton, Henry built a second telegraph line from his house, behind Nassau Hall, to Philosophical Hall. He showed that a “quantity” current could induce an “intensity” current, that is, that voltage could be stepped up and down. This was the theoretical basis for the modern transformer. Still another invention was that of the electromagnetic relay, a crucial development for the telegraph, with which a weak line signal could be boosted along through a circuit. He also developed the basic form of the telegraph receiver. This was not a galvanometer or a magnetized needle, which European telegraphs were employing, but a magnet operating a movable armature which made rapid signalling and audible reception possible. With this work he completed the development of the four component parts of the telegraph: the electromagnet, the series circuit, the relay, and the receiver.

Henry first operated his relay in 1835. In 1839 Samuel Morse asked Henry if he might visit him at Princeton. The deceptively simple device which Morse had conjured up on board the packet ship Sully , in 1832, was still largely undeveloped. “I should come as a learner,” Morse wrote, “I have many questions to ask.” Morse asked, and Henry, in this and other meetings, told everything he knew about the telegraph and the relay which made long-distance transmission possible. In 1843 Henry made his final contribution to Morse’s telegraph system, assuring Morse that his line wire could be insulated by stringing it above ground on glass bureau-knobs. Only then was Morse finally able to send his historic message from the Capitol in Washington to Alfred Vail in Baltimore: “What hath God wrought?” To put the credit where it was fairly due, many think, Morse might instead have asked: “What hath Henry wrought?”

At this promising point in Henry’s career James Smithson changed the whole course of American science by leaving his money to the United States “to found at Washington, under the name of the Smithsonian Institution, an establishment for the increase and diffusion of knowledge among men.” Congress then proceeded to debate the function of the projected Institution for almost a decade. For the question arose, what was the Smithsonian to be? Although Smithson himself had obviously contemplated a scientific institution, all sorts of schemes were proposed: art center, library, museum, even a mint.

As the foremost scientist in the nation, Henry was immediately consulted by the Board of Regents appointed by Congress. He proposed that to “increase” knowledge the institution should engage in research in various branches of learning; to “diffuse” knowledge it should publish periodicals and reports so that the results of its research could be made known to all men.

Henry’s plan for the Smithsonian was accepted by the Board. Then, after canvassing some of the world’s greatest scientists, including Faraday and François Arago (who had been a friend of Smithson’s), the Regents invited Henry to assume the secretaryship.