Joseph Henry - Early years, The Albany Academy, Influences in Aeronautics, Influences in Room Acoustics, Career, Further reading

Physicist, born in Albany, New York, USA. He worked as a tutor, then as a surveyor (1825–6) before becoming a professor at his alma mater, Albany Academy (1826–32). He began research on electromagnetism (1827), constructed the first electromagnetic motor (1829), and discovered electrical induction independent of English physicist Michael Faraday. The henry unit of inductance is named after him. He continued his research after transferring to Princeton (1832–46), demonstrating the oscillatory nature of electrical discharges (1842), and diversifying into the fields of astronomy, galvanometry, and telegraphy. In 1846 he was named first secretary and director of the Smithsonian Institution, and through his leadership (1846–77) it supported internationally cooperative scientific research. While administrative duties left him little time for the ‘pure’ scientific endeavours he favoured, he introduced a system of weather forecasting, investigated the propagation of light and sound waves by lighthouses, and encouraged the museum's patronage of anthropology and ethnology.

Joseph Henry (December 17, 1797 – May 13, 1878) was a Scottish-American scientist.

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

Early years

Joseph Henry was born on December 17th, 1797 in Albany, New York to two immigrants from Scotland, Ann Alexander Henry and William Henry. For the rest of his childhood, Joseph lived with his grandmother in Galway, New York. He attended a school which would later be named Joseph Henry Elementary School in his honor.

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 by Principal T. He was the first to coil insulated wire tightly around an iron core in order to make an extremely powerful electromagnet, improving on William Sturgeon’s electromagnet, which used loosely coiled uninsulated wire. 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.

He took what he had learned a step further and, in 1831, created one of the first machines to use electromagnetism for motion. 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.

Here, he also discovered the property of self inductance.

Influences in Aeronautics

Prof. Henry was introduced to Prof. Thaddeus Lowe, a balloonist from New Hampshire who had taken interest in the phenomena of lighter-than-air gases, and exploits into meteorology, in particular, the high winds which we call the Jet stream today. Henry took a great interest in Lowe's endeavors so much as to support and promote him among some of the more prominent scientists and institutions of the day.

In June of 1860, Lowe had made a successful test flight with his gigantic balloon, first named the City of New York hence renamed The Great Western, flying from Philadelphia to Medford, New York. Henry convinced Lowe to take his balloon to a point more West and fly the balloon back to the eastern seaboard, an exercise that would keep his investors interested.

Lowe took several smaller balloons to Cincinnati in March 1861. With the Southern States seceding from the union, and the onset of civil war, Lowe abandoned further attempts at a transatlantic crossing and, with Henry's endorsement, went to Washington to offer his services with use of balloons. Joseph Henry submitted a letter to the Secretary of War, Simon Cameron showing his endorsement:

On Henry's recommendation Lowe went on to form the Union Army Balloon Corps and served two years with the Army of the Potomac as a Civil War Aeronaut.

Influences in Room Acoustics

Over 150 years ago, Joseph Henry identified the room acoustics phenomena we now call direct sound, early reflections, and reverberation. He demonstrated the early sound integration period and laid the ground work for further fundamental research on early reflections that was not followed up until the work at Gottingen University in the 1950-1960’s.

Joseph Henry devised a beautifully simple experiment to demonstrate the integration of direct and early sound. He gradually approaches the wall, clapping, until no echo is perceived, at a distance of 30 feet – the “Henry Distance” – equating to an early sound integration time of 60 ms. [An auralization of Henry's experiment]

Career

1826 - Professor of Mathematics and Natural Philosophy at The Albany Academy, New York. The Joseph Henry Press, a publication arm of the NAS, is named for him.

Further reading

Ames, Joseph Sweetman (Ed.), The discovery of induced electric currents, Vol. Memoirs, by Joseph Henry. New York, Cincinnati [etc.] American book company [c1900] LCCN 00005889 Coulson, Thomas, Joseph Henry: His Life and Work, Princeton, Princeton University Press, 1950. Henry, Joseph, Scientific Writings of Joseph Henry. Moyer, Albert E., Joseph Henry: The Rise of an American Scientist, Washington, Smithsonian Institution Press, 1997.