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....
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