Joseph Henry

Joseph Henry lived from 1797 to 1878. Of Scottish decent, Henry was a son of a day laborer in Albany, New York. He was sent to live with his grandmother as a small boy in a village about 40 miles from Albany. At the age of thirteen, be became apprenticed to a watchmaker. He then became interested in theatre and was offered employment as a professional actor, but instead he attended Albany Academy where he was provided with free tuition.

He has always been interested in science and by 1823 his education was very far advanced that he was assisting the teaching of science courses. By 1826, after a shift as a district schoolteacher and as a private tutor, he was appointed Professor of Mathematics and Natural Philosophy at Albany Academy. With all these titles and positions eh received, Joseph Henry still managed to do important scientific experiments. Joseph Henry became specifically interested in terrestrial magnetism.

His interest in this led him to experiment with electromagnetism. His apprenticeship as a watchmaker stood him in a good stead in the construction of batteries and other contraptions. Although there had been other physicists who had observed the magnetic effects from electrical currents, Henry was the first to wind insulated wires around an iron core to obtain powerful electromagnets. Before he left Albany, he built one for Yale that would lift 2,300 pounds, which was the largest in the world in that time period.

In experimenting with magnets, Henry observed the large spark that was generated when the circuit was broken, and figured out the property known as self-inductance, or the inertial characteristic of an electrical circuit. If a current is flowing, self-inductance tends to keep it from building up. Henry found that self-inductance is greatly affected by the configuration of the circuit, especially the coiling of the wire. He also discovered how to make non-inductive windings by folding the wire back on itself. At the same time Henry was doing all this, another physicist, Michael Faraday was doing similar work in England.

Henry was slow in publishing his results and was unaware of Faraday’s work, therefore Faraday is recognized as the discoverer of mutual inductance, which is the basis of transformers, while Henry is only accredited for the discovery of self-inductance. At the age of 35, Yale’s geologist, Benjamin Silliman, was consulted regarding the possible appointment of Henry to Princeton. Silliman’s response was negative in saying that Henry has no superior in our country, and Henry, who was modest, defended the fact that he never graduated any colleges and he is principally self-educated.

Henry therefore got the job. His initial salary at Princeton was $1,000 per annum plus a house. The Trustees also provided for $100 for the purchase of a new electrical machine. At Princeton, Henry worked with his brother-in-law, Stephen Alexander, in the observation of sunspots and continued his own work on magnets, building Princeton an even larger magnet that would lift 3,500 pounds. He also arranged two long wires, one in the front of Nassau Hall and one behind so that he was able to send a signal by induction through the building.

Another wire from is lab in Philosophical Hall to his home on the campus was used to send signals to his wife. This signal used a remote electromagnet to close a switch for a stronger local circuit. S. F. B Morse used a similar arrangement in his invention, the telegraph. Henry not only taught physics (natural philosophy), but he also taught chemistry, geology, mineralogy, astronomy, and architecture. Princeton gave Henry an opportunity to travel abroad on leave at full salary. In 1837, he met Faraday, Wheatstone, and other British scientists.

They interchanged ideas and Henry returns back to Princeton with a variety of scientific equipment purchased. During his remaining years in Princeton, Henry continued his electrical investigations, but also branched out into study of phosphorescence, sound, capillary action, and ballistics. In 1844, he was a member of a committee to investigate the explosion of a gun during a demonstration of the new U. S. S. Princeton. His experiments on gun castings on this committee led him into the subject of the molecular cohesion of matter.

In 1872, John C. Green, founder of the school of Science at Princeton, endowed a chair of physics in Henry’s honor. A century later, when the main physics building, Jadwin Hall, was dedicated in 1970; the Physics Department manifested its continuing esteem for Henry by declaring that all of the laboratory facilities housed in Jadwin and Palmer Halls and Elementary Particles Laboratory should be collectively known as the Joseph Henry Laboratories. Some of Henry’s laboratory equipment is on display in the lobby of Jadwin Hall.

In Washington, his statute stands before the old Smithsonian Building. Henry was one of the original members of the National Academy of Sciences and served as its second president. He was also a trustee of Princeton and president of the American Association for the Advancement of Science. When he died in 1878, his funeral was attended by the president of the United States with his cabinet, the chief justice and associate justices of the Supreme Court, by many members of both houses of Congress, and by many scientists and other illustrious personages.


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