Henry, Joseph (1797-1878)

Joseph Henry (1797-1878)

Source

Physicist

Early Years. Joseph Henry was born in Albany, New York, in 1797. His working-class family often struggled for money, and in his early teens Henry began working as a store clerk. He also served as an apprentice to a jeweler and watchmaker, and in his extra time he acted and wrote plays for an amateur theatrical group. Reading a popular book on natural science, he became so fascinated by the subject that he committed himself to becoming a scientist. He studied assiduously, was admitted as a student at the Albany Academy, and in 1826 became professor of mathematics and natural philosophy at that institution.

Henry’s Early Experiments. As a professor Henry made important advances in the study of electromagnetism. A British scientist, William Sturgeon, had invented the electromagnet in 1825, but Henry improved the device to its present-day form. Sturgeon had wrapped bare copper wire around a bar of soft iron; when a current was sent through the wire, the iron produced enough magnetic force to lift a nine-pound piece of iron or steel. By using insulated rather than bare wire Henry was able to lift heavier weights. Like Henry, the British scientist Michael Faraday experimented with electromagnetism. In 1831 Faraday discovered that the iron core of the electromagnet, when moved in and out of its surrounding copper coils, produced electricity in the wire—a phenomenon known as electromagnetic induction. It appears that Henry had discovered induction before Faraday but failed to publish his observations; he did not do so until three months after Faraday’s findings appeared in the April 1832 issue of Uve Annals of Philosophy. The work of both men was important for the development of the electric-power industry in the nineteenth century.

Telegraphic Experiments. During his years at the Albany Academy, Henry also discovered that the arrangement of the wire coils of an electromagnet affected its strength and durability. Using two different coil arrangements, he created two electromagnets, which he called a quantity magnet and an intensity magnet. Using the intensity magnet, Henry transmitted signals through a wire three miles in length. He published his findings in the American Journal of Science in 1831. Later in the 1830s Samuel Morse improved on Henry’s device by inventing the relay, which allowed the signal to be transmitted over longer distances, and the Morse Code, which made it possible for letters to be translated into electrical impulses and vice versa. Morse patented this invention in 1844 as the telegraph.

Other Inventions. Henry also invented an electric motor while at Albany Academy. He balanced an electromagnetic bar horizontally on a pivot; below each end of the bar was a vertical permanent magnet. Two wires extended from each end of the bar; when the bar was tilted in either direction the wires on that end made contact with the terminals of a battery, thereby sending current through the wires and producing magnetism in the bar. The permanent magnet on that end was arranged so that the pole nearest the bar was of the same polarity as that end of the electromagnet; since magnets of the same polarity repel each other, the bar would tilt the other way, breaking the connection with the battery on that end and establishing a connection with the battery on the other end. That end of the bar would then be repelled by the permanent magnet below it, and the electromagnet would tilt back the other way, and so on. During one experiment the oscillation continued for more than an hour. In 1832 Henry accepted a professorship in natural philosophy at the College of New Jersey in Princeton, where he not only continued to make important discoveries in electromagnetism but also conducted studies in solar physics and other branches of physics.

The Smithsonian Institution. When the Englishman John Smithson, who had never been to America, died in 1829 he bequeathed more than half a million dollars to the United States to found an institution “for the increase and diffusion of knowledge among men.” Congress established the Smithsonian Institution in 1846, and Henry, the best-known scientist in America at the time, was named as its secretary, or head. Throughout his tenure Henry emphasized the necessity of original research, ensuring that the Smithsonian would be not just a natural science museum but a research institution. He introduced such innovations as the production of weather forecasts (especially storm warnings) based on reports of weather conditions obtained by telegraph. Henry remained secretary of the Smithsonian until his death in 1878. He also helped establish the American Association for the Advancement of Science in 1847 and served as president of this organization from 1868 until he died.

Sources

Thomas Couison, Joseph Henry: His Life and Work (Princeton: Princeton University Press, 1950);

Bernard Jaffe, “Joseph Henry,” in his Men of Science in America: The Role of Science in the Growth of Our Country (New York: Simon &, Schuster, 1944).