XXVII 

 JOSEPH HENRY 



1797-1878 



Bom at Albany, New York, December i/, 1797, Joseph Henry pre- 

 pared jor the profession of inedicine, but an appointment as an a-^~ 

 sistant engineer on the state road diverted his interests toward me- 

 chanics. In 1826 he was appointed instructor of physics at Albany 

 Institute, nozv the Albany Boys Academy, where he conducted his first 

 experiments in electricity. In 1828 he first produced a strong electro- 

 magnet by winding fine insulated wire around a piece of soft iron, 

 and soon succeeded in exciting his electro-magnet at a distance by the 

 use of high intensity batteries made up of many cells. Demonstrat- 

 ing that the nmnber of coils of fine wire about a magnet had as much 

 influence as the intensity of the current and that after winding many 

 coils around the soft iron magnet it could still be made magnetic, he 

 suggested the principle which Morse later used in the telegraph. In 

 18^2 he discovered that in a long conductor the primary current, by 

 an induction upon itself, produced a number of secondary currents 

 that greatly increased the intensity of the discharge. 



He was appointed professor of natural philosophy at Princeton 

 University in 18^2 and became secretary of the Smithsonian Institu- 

 tion in 1846. He died in Washington, May ij, 1878. 



ON THE PRODUCTION OF CURRENTS AND SPARKS OP! 

 ELECTRICITY FROM MAGNETISM * 



Although the discoveries of Oersted, Arago, Faraday, and others, 

 have placed the intimate connection of electricity and magnetism in a 

 most striking point of view, and although the theory of Ampere has 

 referred all the phenomena of both these departments of science to the 



* Silliman's American Journal of Science, July, 1832, Vol. XXII, pp. 403- 

 408; Scientific Writings, Vol. I., p. yz- 



198 



