Joseph Henry

From Freepedia

Joseph Henry (December 17 1797 – May 13 1878) was an American scientist. During his lifetime, he was considered the greatest American scientist since Benjamin Franklin. While building electromagnets, he discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance, independently of Faraday, but Faraday was the first to publish his results. His work on the electromagnetic relay was the basis of the electrical telegraph, jointly invented by Morse and Wheatstone.

The SI unit of inductance, the henry, is named after him.

Contents 1 Early Years 2 At The Albany Academy 3 Career 4 See also

Early Years

Joseph Henry was born on December 17th, 1797 in Albany, NY to two immigrants from Scotland, Ann Alexander Henry and William Henry. His parents were poor and Joseph’s father died while he was still a young boy. So, for the rest of his childhood, Joseph lived with his grandmother in Galway, NY. He attended a school which would later be named Joseph Henry Elementary School in his honor. After school, he worked at a general store, and later, at the age of thirteen, he went to work as an apprentice watchmaker and silversmith. Joseph’s first love was theater and he came very close to becoming a professional actor. His interest in science was piqued at the age of sixteen, by a book of lectures on scientific topics titled Popular Lectures on Experimental Philosophy. And, in 1819, persuaded by some influential friends to pursue a more academic career, he entered Albany Academy, where he was given free tuition. He was poor so, even with free tuition, Joseph Henry had to support himself with teaching and private tutoring positions. Initially, he intended to go into the field of medicine, but, in 1824, he was appointed an assistant engineer for the survey of State road, being constructed between the Hudson River and Lake Erie (a distance of 300 miles). From then on, he was inspired to a career in civil or mechanical engineering.

At The Albany Academy

Joseph Henry excelled at his studies (so much so, that he would often be helping his teachers teach science) and, by 1826, he was appointed Professor of Mathematics and Natural Philosophy at The Albany Academy. Some of Henry's most important research was conducted in this new position. Joseph’s curiosity about terrestrial magnetism lead him to experiment with magnetism in general. He was the first to tightly coil insulated wire around a ferrous core to make an extremely powerful electromagnet, improving on William Sturgeon’s electromagnet, which used loosely coiled uninsulated wire. Using this technique, he built the most powerful 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 used. The latter made the telegraph feasible.

He took what he had learned a step further and, in 1831, created one of the first machines to use electromagnetism for motion. This was the earliest ancestor of modern DC motor. It didn’t make use of rotating motion, but was merely an electromagnet perched on a pole, rocking back and forth. The rocking motion was caused by on 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.

Here, he also discovered the property of self inductance. But, around the same time, a British scientist by the name of Michael Faraday had discovered it as well and was quicker to publish his results, becoming the officially recognized discoverer of the phenomenon.

Career

• 1826 - Professor of Mathematics and Natural Philosophy at Albany Academy, New York.
• 1832 - Professor at Princeton.
• 1835 - invents the electromechanical relay.
• 1846 - First secretary of the Smithsonian Institution, who contended with the notorious antics of the Megatherium Club.
• Second president of National Academy of Sciences.

See also

• Electromagnetism: Henry (Scientific units named after people), Multiple coil magnet

• Published physics papers - On the Production of Currents and Sparks of Electricity from Magnetism and On Electro-Dynamic Induction (extract)

• Lists: List of physicists, Timeline of invention, Timeline of communication technology, List of physics topics
• Other: Gasport, New York, American Philosophical Society