HENRY
Henry's parents both came to America from Scoitland as children in the turbulent year 1775. His father, a poor laborer, died when the son was still a boy, and young Henry was soon apprenticed out to a watchmaker and silversmith in Albany, New York. Nothing distinguished Henry from other half-educated young craftsmen except strong interests in amateur theater and in reading. But at the age of sixteen he chanced to read a book of Popular Lectures on Experimental Philosophy, Astronomy, and Chemistry. Fascinated by this glimpse of science, he resolved to learn more.
In 1819 he enrolled in the Albany Academy. In modern terms this would be closest to a private secondary school, but in early American terms it offered the equivalent of a college education. Henry went beyond the coursework, avidly reading books in every area of science and many other fields. He meanwhile made use of each increment in his learning to support himself, progressing from country schoolmaster through tutor of wealthy youths and road surveyor to Professor of Mathematics and Natural Philosophy at the Albany Academy.
A few years later he described his situation in a letter: ". . . My duties at the Academy are not well suited to my taste. I am engaged on an average seven hours in a day, one half of the time in teaching the higher classes in Mathematics, and the other half in the drudgery of instructing a class of sixty boys in the elements of Arithmetic." Nevertheless he found a little time, a little space, and a little money to do research.
Like most scientists of his day Henry was no specialist, and matters like meteorology took his attention throughout his life. At the Albany Academy he prospected in various areas of physical science and almost at once struck his vein of gold: electromagnetism. He was inspired in part by reports of a rudimentary electromagnet constructed in Europe and in part by theoretical ideas based on his reading of Ampere. He began to build electromagnets which, for the first time, were wound with many strands and layers of insulated wire. (According to legend, for insulation he used silk strips torn from his wife's petticoats.) He carefully distinguished between "quantity" circuits of high amperage and "intensity" circuits of high voltage; he worked out what we now call impedance matching; he independently found a preliminary sort of Ohm's law. Understanding electrical circuits better than any of his predecessors, he built an electromagnet that could hold up to 750 pounds of iron, yet required a battery of only modest size and cost.
Electromagnets of such efficiency were a marvelous new tool for science. Henry used them to build "philosophical toys" which foreshadowed the telegraph and the electric motor. The strong magnetic fields were equally valuable for fundamental research and allowed him to discover mutual induction and self-induction. All this soon brought Henry international fame. His reputation would have been still greater had it not been for Faraday, who, with equal genius and better working conditions in England, had anticipated some of Henry's discoveries.
In 1832 Henry went to Princeton (then called the College of New Jersey) as professor of natural philosophy, one of the handful of positions in America which would give a physicist enough time for research. Here he did much solid work on electricity and magnetism and also published papers on capillarity, phosphorescence, the heat of sunspots, the aurora, and more. He was widely respected, usually a reticent man but outspoken when the needs of science were at stake. Throughout his life he held devoutly to the Presbyterianism in which he was raised. Over the years he attracted a number of close friends; he worked with them to raise the level of pure science in America, which they considered dismally low.
In 1846 he accepted the post of Secretary in the new and unformed Smithsonian Institution. Much of his life thereafter was spent in giving governmental bodies scientific advice, particularly on practical matters, and in working to keep the Smithsonian from becoming a purely curatorial institution. As director of the Smithsonian and as President of the fledgling National Academy of Sciences from 1867 to his death, Henry worked to ensure that America would support science—not only applied but also pure science, not only amateur but also rigorous and professional science.
The following excerpt is from the American Journal of Science (vol. 22, 1832, p.403-08), published by Benjamin Silliman of Yale, a magazine which for many decades was the leading American scientific journal. The second selection is part of a longer work presented to the American Philosophical Society and published in its Transactions (n.s. vol. 6, 1839, p. 303-37); it shows Henry masterfully dealing with the problem of induction and electrical currents, using no detecting instrument more sensitive than the human body.
