Joseph Henry.

Joseph Henry (December 17, 1797 - May 13, 1878) was a Scottish-American scientist who served as the first Secretary of the Smithsonian Institution. During his lifetime, he was considered one of the greatest American scientists since Benjamin Franklin. While building electromagnets, Henry discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance independently of Faraday, though Faraday was the first to publish his results. Henry's work on the electromagnetic relay was the basis of the electrical telegraph, jointly invented by Samuel Morse and Charles Wheatstone. The SI unit of inductance, the henry, is named after Joseph Henry.

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. His parents were poor, and Joseph's father died while he was still a young boy. 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. 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 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. He was so poor, even with free tuition, that he had to support himself with teaching and private tutoring positions. He intended to go into the field of 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 civil or mechanical engineering.

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. Romeyn Beck. Some of his most important research was conducted in this new position. His curiosity about terrestrial magnetism lead him to experiment with magnetism in general. 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. 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. 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 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. Here, Henry also discovered the property of self inductance. Around the same time, the British scientist Michael Faraday discovered it as well and, being first to publish his results, became the officially recognized discoverer of the phenomenon.

In 1848 Joseph Henry worked in conjunction with Professor Stephen Alexander to determine the relative temperatures for different parts of the solar disk. Using a thermopile, they determined that sunspots were cooler than the surrounding regions. This work was shown to the astronomer Angelo Secchi who extended it, but with some question as to whether Henry was given proper credit for his own earlier work.

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. He brought a robust scientific approach to the subject of acoustics - a subject which is plagued by misunderstanding and misinformation to this day.

Joseph Henry devised a beautifully simple experiment to demonstrate the integration of direct and early sound. A listener, standing in an open space 100 feet from a wall, claps his hands and hears an echo. 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.

Later years.
As a famous scientist and director of the Smithsonian Institution, Henry received visits from other scientists and inventors who sought his advice. Henry was patient, kindly, self-controlled, and gently humorous. One such visitor was Alexander Graham Bell who on March 1, 1875 carried a letter of introduction to Henry. Henry showed an interest in seeing Bell's experimental apparatus and Bell returned the following day. After the demonstration, Bell mentioned his untested theory on how to transmit human speech electrically by means of a "harp apparatus" which would have several steel reeds tuned to different frequencies to cover the voice spectrum. Henry said Bell had "the germ of a great invention". Henry advised Bell not to publish his ideas until he had perfected the invention. When Bell objected that he lacked the necessary knowledge, Henry firmly advised: "Get it!"

On June 25 1876, Bell's experimental telephone (using a different design) was demonstrated at the Centennial Exhibition in Philadelphia where Joseph Henry was one of the judges for electrical exhibits. On January 13, 1877 Bell demonstrated his instruments to Henry at the Smithsonian Institution and Henry invited Bell to show them again that night at the Washington Philosophical Society. Henry praised "the value and astonishing character of Mr. Bell's discovery and invention."

Henry died on May 13, 1878 and was buried a few days later in Oak Hill Cemetery in northwest Washington, D.C.

Source Wikipedia.