JOSEPH HENRY. 359 



being called the next year to be Professor of Natural Philoso- 

 phy in the College of New Jersey, now Princeton University. 



His researches were interrupted for a year or more when he 

 removed to Princeton. At first he had his new course of lec- 

 tures to prepare, and in 1833 he supplied the place of the Pro- 

 fessor of Chemistry and Geology, Dr. Torrey, during the 

 absence of the latter in Europe. When he was able to resume 

 his experiments, Faraday was running neck and neck with him 

 on the same course. Several important discoveries were made 

 by both men independently. In August, 1829, Henry had 

 made in Albany the discovery of electrical self-induction in 

 a long helical wire the extra current as it is called in ad- 

 vance of Faraday, who made independently the same discov- 

 ery in 1834. He also made independently of Faraday the 

 great discovery of magneto-electricity. In Princeton, with 

 some coils of insulated copper ribbon these coils are known 

 in electrical text-books as "Henry's coils" he pursued 

 the subject, until he discovered that one induced current can 

 produce another, the second current a third, the third a 

 fourth, the fourth a fifth ; also that a current of quantity 

 may be produced by one of intensity, and the converse ; 

 also that currents can be induced at a distance, and from 

 obtaining currents in one room induced from primary cur- 

 rents in another room, with no connection merely by the dis- 

 turbance of the electrical plenum, he passed to the accomplishment 

 of the same result between an upper room of the Philo- 

 sophical Hall and the cellar of the same building ; then be- 

 tween two parallel wires stretched perpendicularly, several 

 hundred feet apart, and then, connecting the tinned roof of 

 his house with the ground, he magnetized needles in his libra- 

 ry, by induction, from a thunder cloud eight miles away. The 

 practical applications of these discoveries are numerous. In 

 1836, when in these experiments a Leyden jar was substituted 

 for galvanism, these coils led Henry to the discovery of the 

 oscillatory character of the electric discharge. They were 

 also used to investigate electric screening, which Henry at- 

 tributed to the neutralizing action of a current induced in the 

 interposed body. These discoveries were announced in the 

 years 1834, 1835, 1836, and 1838. Before leaving Albany Henry 

 had been employed to make one of his powerful magnets for 

 the laboratory of Yale College, then under the direction of Prof. 



