PHILOSOPHICAL SOCIETY OF WASHINGTON. 255 



(which should be terminated by cups of mercury) are connected 

 by a copper wire not more tlian a foot in length, no spark is per- 

 ceived wlien the connection is either formed or broken : but if a 

 wire thirty or forty feet long be used (instead of the short wire), 

 though no spark will be perceptible when the connection is made, 

 yet when it is broken by drawing one end of the wire from its 

 cup of mercury, a vivid spark is produced. . . . The effect 

 appears somewhat increased by coiling the wire into a helix: it 

 seems also to depend in some measure on the length and thick- 

 ness of the wire. I can account for these phenomena only by 

 supposing the long wire to become charged with electricity which 

 by its reaction on itself projects a spark wlien the connection is 

 broken."* This is the earliest notice of the curious phenomenon 

 of self-induction in an electric discharge. 



Election as Professor at PiHnceton. — The Trustees of the 

 College of New Jersey at Princeton, were about this time in 

 search of a Professor to fill the chair of Natural Philosophy in 

 that College, made vacant by the resignation of Professor Henry 

 Vethake, wiio had accepted a Professorship of Natural Philosophy 

 in the recently established University of the City of New York. 

 Professor Henry had already won considerable I'eputation as a 

 lecturer and teacher, no less than as an experimental physicist. 

 Professor Silliman of Yale College, urging his appointment, 

 wrote : " Henry has no superior among the scientific men of the 

 country." And Professor Renvvick of Columbia College (New 

 York) still more emphatically added : "He has no equal." 



Professor Henry was unanimously elected by the Trustees ;f 

 and he accepted the appointment : although strongly attached to 

 his first Academy, endeared to him by early memories, by six 

 years of successful labors, and by the warm regard of all his 

 associates. May it not be added that his residence at the capital 

 of the State of New York, was further endeared to him by life's 

 romance, — a most congenial and happy marriage contracted in 

 1830. 



ELECTRICAL RESEARCHES AT PRINCETON : FROM 1833 TO 1842. 



In November 1832, Henry left the scene of his early scientific 

 triumphs, the Albany Academy, and removed to Princeton with 

 his family. For a year or two he gave his whole attention and 



* Silliman's Am. Jour. Sci., July, 1832, vol. xxii. p. 408. 



f Dr. Maclean connected with the Faculty of the College of New .Jersey 

 at Piiuceton for fifty years, and for fourteen years its venerable president, 

 in his History of tlie College (2 vols. 8vo. Philadelphia, 1877,) gives a 

 Very interesting account of the appointment and election of Joseph Henry 

 as Professor of Natural Philosophy in 1832, vol. ii. pp. 288-291. 



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