Professor Henry And His Philosophical Toys


He did well enough. At sixteen he was elected president of the Rostrum, an amateur theatrical group for which he wrote, produced, and acted. In the very same year, however, he renounced this second career. He had become intrigued by a book, Gregory’s Lectures on Experimental Philosopliy, Astronomy and Chemistry . It was this, he later recalled, that “fixed my attention upon the study of nature.”

Gregory, an English clergyman, used the question technique to arouse his readers’ interest: “You throw a stone or shoot an arrow into the air; why does it not go forward in a line with the direction you give it? Why does it stop at a certain distance and then return … Again you look into a clear well of water and see your face and figure, as if palmed there. Why is this?” The book in which he found these riddles, largely solved by Isaac Newton a century before, was, as Henry later put it, “by no means a profound work.” But it introduced him to an exciting world in which both his imagination and his reason could play a part.

Plagued by a sketchy education, Henry enrolled in night classes at the Albany Academy, a school so highly ranked at the time that Dr. Eliphalet Nott, president of Union College, called it “a college in disguise.” To pay for his courses Henry first taught grammar in a local school district, then became tutor to General Stephen van Rensselaer’s family. In the years following he diligently studied botany, medicine, chemistry, mathematics, and geology. In 1824 he read his first scientific paper before the Albany Institute, an informal scientific society of some 250 members, on “The Chemical and Mechanical Effects of Steam.” It was an apt subject for an audience that lived on a river bustling with steamboats.

On the side young Joseph Henry tutored Henry James, the future father of William, the psychologist, and Henry, the novelist. To recover his health, strained by the double effort of teaching and studying, he spent a year as a surveyor laying out a road between West Point and Lake Erie. Then, in 1826, he was offered the chair of mathematics and natural philosophy at the Albany Academy.

In the next seven years Henry performed nearly all the experiments for which he was to be remembered. It was the only period in his life when he was sufficiently tree to devote himself to original research. Yet compared with Faraday, who was working on the same problems with the splendid equipment of the Royal Society in London, Henry had little time and inadequate facilities. Most of his work was done at night or during the summer recess when his teaching duties were over and the “laboratory”—a vacant classroomwas at his disposal.

In his first experiments Henry decided to probe the nature of magnetism and electricity, an original choice for several reasons Alter Franklin, electricity had become more of a laboratory diversion than a matter for serious study. In America, knowledge of the subject had almost stood still for a quarter of a century. Moreover, as Henry noted at the time, there was an economic reason for its unpopularity. The primitive batteries of the day and the zinc, acids, and copper wire that went into the necessary apparatus were scarce and expensive. Nevertheless, Henry marked it as a “most fruitful field of discovery”; and perhaps he selected electricity for research simply because, as he said, it was “less generally understood in this country than almost an) other department of natural science.”

At the time liule was known about the connection between electricity and magnetism or if, indeed, any connection existed. So little was known, in fact, that electricity was being generated long before an explanation for its behavior had even begun to evolve.

In 1786 the Italian anatomist Luigi Galvani constructed a primitive electric cell from two different metals and the natural fluids in a dissected frog. But Galvani supposed, in a deduction that was not unreasonable at the time, that the electrical current was coming from the animal itself. Ten years later the physicist Alessandro VoIla eliminated the frog and built a “voltaic pile,” or battery, out of zinc and copper discs placed alternately on top of one another and interleaved with discs of moistened paper. With this continuous source of current at their disposal scientists were able to do away with the old Leyden jar, the electrostatic machine used by Franklin and his colleagues, which produced only a momentary spark.

In 1802 another Italian, Gian Domenico Romagnosi, noticed thai a current (lowing through a wire caused a magnetic needle to line up perpendicularly to the wire. The scientific world ignored the implications of this discovery until 1822, when Hans Oersted, of the University of Copenhagen, rediscovered the effect. Shortly afterward the Englishman William Sturgeon put this relationship between electricity and magnetism to work in an electromagnet. Varnishing an iron bar (for insulation), he wrapped it with copper wire and connected the wire to the terminals of a voltaic battery. This crude device lifted a few pounds of iron.

Oersted and Sturgeon had graphically shown that electricity could produce magnetism. The question was whether the reverse effect—electricity from magnetism—could be obtained. Faraday, fully familiar with the European experiments, thought that it could. In 1822 he wrote confidently in his notebook: “Convert magnetism into electricity.”