Joseph Henry | Biography

Joseph Henry was born on December 17, 1797, in Albany, New York. Henry's family was poor; his father could not afford to send his son to school, so the boy received a very limited education.

According to legend, in 1813 Henry chased his pet rabbit under a church. While crawling around, Henry noticed some floorboards were missing and crawled up into the church. There he came across a shelf of books and began browsing. One book, Lectures on Experimental Philosophy, got him hooked on science. He took a job teaching at a country school to earn money and enrolled at the Albany Academy. He intended to study medicine, but he had a job offer as a surveyor, and this aimed him toward engineering. In 1826 he was still at the Albany Academy, but as a teacher in the subjects of science and mathematics.

Meanwhile, in 1820, Danish Physicist Hans Christian Oersted had made the discovery that the flow of an electric current through a wire produced a magnetic field. This led other scientists to experiment as well, among them Henry and English physicist Michael Faraday. There were some remarkable parallels between Henry and Faraday; they vied with each other in claiming priority in their discoveries.

In 1829 Henry learned of the electromagnet that had been invented by William Sturgeon (1783-1850) and decided he could improve on it. While Sturgeon's was able to lift nine pounds (four kg), Henry's 1831 version could lift 750 pounds (340 kg). Later that same year he lifted 2,000 pounds (900 kg) during a demonstration at Yale and was appointed a professor as a reward. He also built small electromagnets and devised an electrical relay system.

Henry gave advice and help freely; he met with one man who knew nothing about science but was very interested in electromagnetism. The man, Samuel Morse (1791-1872), learned a great deal from Henry, then proceeded to take out a patent in 1840 for the telegraph and make a fortune. Prior to that, Henry had a long conference with Charles Wheatstone (1802-1875), who then patented the telegraph in England in 1837. These irritants were nothing, however, when compared to what happened in 1831.

The story actually begins in 1830. Teaching at the Albany Academy monopolized Henry's time to such an extent, he had only the month of August in which to conduct research and experiment. In August of 1830 Henry discovered the principal of electric induction, the process in which an electric current in one coil of wire can set up a current in another coil. If the flow of electricity can produce a magnetic field, he reasoned, a magnetic field should be able to induce an electric current.

When the end of August arrived, Henry had not completed his investigation. He decided to set the work aside and return to it the following August. It was with considerable shock that Henry read Michael Faraday's announcement in 1831 of the discovery of electric induction.

Rushing back to his experiments, Henry published a report of his own discovery, but he was too late; Faraday received credit for the discovery. To his own credit, Henry never argued about Faraday's priority. He believed scientific discoveries belonged to all the world and never sought patents for any of his work.

Henry did include one item in his paper that Faraday had missed: self-induction. A coil carrying electric current not only induces a flow in another coil, it can induce a current in itself. In 1834 Faraday discovered self-induction independently, but this time Henry got the credit. Estonian physicist Heinrich Lenz (1804-1865) also made the discovery independently and took it farther than both Henry and Faraday. Self-inductance became an important part in the design of electric circuits.

In 1842 Henry anticipated a discovery that has been credited to Heinrich Rudolph Hertz. Henry discovered that he could magnetize needles in a basement with an electric spark from two floors above, correctly ascribing it to electromagnetic wave propagation.

In addition to describing the mechanism of an electric motor, which wouldn't be practical until Faraday invented his generator to produce a constant electric current, Henry was involved in many other endeavors. In 1846 he was appointed first director of the new Smithsonian Institution. Two years later he projected the image of the sun on a screen, made careful measurements of temperature, and discovered that the mysterious sunspots were relatively cooler than the rest of the sun.

Putting the telegraph to its first scientific task, Henry obtained weather reports from all over the country. His study of meteorology eventually led to the establishment of the United States Weather Bureau.

On May 13, 1878, Joseph Henry died. His name was honored in 1893 when the unit of electrical inductance was named the "henry."