Joseph Henry, Pioneer in Space Communication

Joseph Henry, while a teacher at the Albany Academy, brought the electromagnet to its present form and distinguished two types, the "quantity" magnet and the "intensity" magnet. He used the intensity magnet in a circuit containing a mile of wire and rang a bell by sending a current through the circuit. His inventions and discoveries cover the essential features of the electromagnetic telegraph. In the period Henry spentin Albany, he probably observed the induced current, at a date set by his daughter, Miss Mary A. Henry, as early as 1830, but he postponed publication and before the larger magnet and coil which he was building were ready for use he learned that Faraday had anticipated him in this most important discovery. Henry came to Princeton in 1832, and there constructed a great magnet for the college, and set up a telegraph line between his laboratory and his house. He also resumed his study of the current of self-induction, which he had noticed in Albany. After spending a year's leave of absence in Europe, he settled to a definite field in which he made his most important discoveries. He thought that most of the work on electromagnetic induction had been concerned with the relations between the current and the magnetic field, and that no one had properly developed what he called "the purely electrical part of Dr. Faraday's admirable discovery.