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Joseph Henry
Joseph Henry (December 17, 1797– May 13, 1878) was an American physicist and inventor who served as the first secretary of the Smithsonian Institution. He was the secretary for the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. He also served as president of the National Academy of Sciences from 1868 to 1878.
While building electromagnets, Henry discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance independently of Michael Faraday, though Faraday was the first to make the discovery and publish his results. Henry developed the electromagnet into a practical device. He invented a precursor to the electric doorbell (specifically a bell that could be rung at a distance via an electric wire, 1831) and electric relay (1835). His work on the electromagnetic relay was the basis of the practical electrical telegraph, invented separately by Samuel F. B. Morse and Sir Charles Wheatstone. In his honor, the SI unit of inductance is named the henry (plural: henries; symbol: H).
Henry was born in Albany, New York, to Scottish immigrants Ann Alexander Henry and William Henry. His parents were poor, and Henry's father died while he was still young. For the rest of his childhood, Henry lived with his grandmother in Galway, New York. After school, he worked at a general store, and at the age of thirteen became an apprentice watchmaker and silversmith. Joseph's first love was theater, and he came close to becoming a professional actor. His interest in science was sparked at the age of sixteen by a book of lectures on scientific topics titled Popular Lectures on Experimental Philosophy.
In 1819, he entered The Albany Academy, where he was given free tuition. Even with free tuition, he was so poor that he had to support himself with teaching and private tutoring positions. He intended to go into medicine, but in 1824 he was appointed an assistant engineer for the survey of the State road being constructed between the Hudson River and Lake Erie. From then on, he was inspired to a career in either civil or mechanical engineering. Henry excelled academically, even often helping his teachers teach science.
In 1826, he was appointed Professor of Mathematics and Natural Philosophy at The Albany Academy by Principal T. Romeyn Beck. Some of his most important research was conducted in this new position. His curiosity about terrestrial magnetism led him to experiment with magnetism in general. He was the first to coil insulated wire tightly around an iron core in order to make a more powerful electromagnet, improving on William Sturgeon's electromagnet which used loosely coiled uninsulated wire. Using this technique, he built the strongest electromagnet at the time, for Yale. He also showed that, when making an electromagnet using just two electrodes attached to a battery, it is best to wind several coils of wire in parallel, but when using a set-up with multiple batteries, there should be only one single long coil. The latter made the telegraph feasible. Because of his early experiments in electromagnetism, some historians credit Henry with discoveries pre-dating Faraday and Hertz; however, Henry is not credited due to not publishing his work.
Using his newly developed electromagnetic principle, in 1831, Henry created one of the first machines to use electromagnetism for motion. This was the earliest ancestor of modern DC motor. It did not make use of rotating motion, but was merely an electromagnet perched on a pole, rocking back and forth. The rocking motion was caused by one of the two leads on both ends of the magnet rocker touching one of the two battery cells, causing a polarity change, and rocking the opposite direction until the other two leads hit the other battery.
This apparatus allowed Henry to recognize the property of self inductance. British scientist Michael Faraday also recognized this property around the same time. Since Faraday published his results first, he became the officially recognized discoverer of the phenomenon.
From 1832 to 1846, Henry served as the first Chair of Natural History at the College of New Jersey, which is now Princeton University. While in Princeton, he taught a wide range of courses including natural history, chemistry, and architecture, and ran a laboratory on campus. Decades later, Henry wrote that he made "several thousand original investigations on electricity, magnetism, and electro-magnetism" while on the Princeton faculty. Henry relied heavily on an African American research assistant, Sam Parker, in his laboratory and experiments. Parker was a free black man hired by the Princeton trustees to assist Henry. In an 1841 letter to mathematician Elias Loomis, Henry wrote:
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Joseph Henry
Joseph Henry (December 17, 1797– May 13, 1878) was an American physicist and inventor who served as the first secretary of the Smithsonian Institution. He was the secretary for the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. He also served as president of the National Academy of Sciences from 1868 to 1878.
While building electromagnets, Henry discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance independently of Michael Faraday, though Faraday was the first to make the discovery and publish his results. Henry developed the electromagnet into a practical device. He invented a precursor to the electric doorbell (specifically a bell that could be rung at a distance via an electric wire, 1831) and electric relay (1835). His work on the electromagnetic relay was the basis of the practical electrical telegraph, invented separately by Samuel F. B. Morse and Sir Charles Wheatstone. In his honor, the SI unit of inductance is named the henry (plural: henries; symbol: H).
Henry was born in Albany, New York, to Scottish immigrants Ann Alexander Henry and William Henry. His parents were poor, and Henry's father died while he was still young. For the rest of his childhood, Henry lived with his grandmother in Galway, New York. After school, he worked at a general store, and at the age of thirteen became an apprentice watchmaker and silversmith. Joseph's first love was theater, and he came close to becoming a professional actor. His interest in science was sparked at the age of sixteen by a book of lectures on scientific topics titled Popular Lectures on Experimental Philosophy.
In 1819, he entered The Albany Academy, where he was given free tuition. Even with free tuition, he was so poor that he had to support himself with teaching and private tutoring positions. He intended to go into medicine, but in 1824 he was appointed an assistant engineer for the survey of the State road being constructed between the Hudson River and Lake Erie. From then on, he was inspired to a career in either civil or mechanical engineering. Henry excelled academically, even often helping his teachers teach science.
In 1826, he was appointed Professor of Mathematics and Natural Philosophy at The Albany Academy by Principal T. Romeyn Beck. Some of his most important research was conducted in this new position. His curiosity about terrestrial magnetism led him to experiment with magnetism in general. He was the first to coil insulated wire tightly around an iron core in order to make a more powerful electromagnet, improving on William Sturgeon's electromagnet which used loosely coiled uninsulated wire. Using this technique, he built the strongest electromagnet at the time, for Yale. He also showed that, when making an electromagnet using just two electrodes attached to a battery, it is best to wind several coils of wire in parallel, but when using a set-up with multiple batteries, there should be only one single long coil. The latter made the telegraph feasible. Because of his early experiments in electromagnetism, some historians credit Henry with discoveries pre-dating Faraday and Hertz; however, Henry is not credited due to not publishing his work.
Using his newly developed electromagnetic principle, in 1831, Henry created one of the first machines to use electromagnetism for motion. This was the earliest ancestor of modern DC motor. It did not make use of rotating motion, but was merely an electromagnet perched on a pole, rocking back and forth. The rocking motion was caused by one of the two leads on both ends of the magnet rocker touching one of the two battery cells, causing a polarity change, and rocking the opposite direction until the other two leads hit the other battery.
This apparatus allowed Henry to recognize the property of self inductance. British scientist Michael Faraday also recognized this property around the same time. Since Faraday published his results first, he became the officially recognized discoverer of the phenomenon.
From 1832 to 1846, Henry served as the first Chair of Natural History at the College of New Jersey, which is now Princeton University. While in Princeton, he taught a wide range of courses including natural history, chemistry, and architecture, and ran a laboratory on campus. Decades later, Henry wrote that he made "several thousand original investigations on electricity, magnetism, and electro-magnetism" while on the Princeton faculty. Henry relied heavily on an African American research assistant, Sam Parker, in his laboratory and experiments. Parker was a free black man hired by the Princeton trustees to assist Henry. In an 1841 letter to mathematician Elias Loomis, Henry wrote:
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