LETTER OF J. HENRY TO REV. S. B. DOD. 149 



WASHINGTON, D. C., December 4, 1876. 



MY DEAR SIR : In compliance with your request that I would 

 give an account of my scientific researches during my connection 

 with the College of New Jersey, I furnish the following brief state- 

 ment of my labors within the period mentioned : 



I. Previous to my call from the Albany Academy to a pro- 

 fessorship in the College of New Jersey, I had made a series of 

 researches on electro-magnetism, in which I developed the principles 

 of the electro-magnet and the means of accumulating the magnetic 

 power to a great extent, and had also applied this power in the 

 invention of the first electro-magnetic machine ; that is, a mechan- 

 ical contrivance by which electro-magnetism was applied as a motive 

 power. 



I soon saw, however, that the application of this power was but 

 an indirect method of employing the energy derived from the com- 

 bustion of coal, and, therefore, could never compete, on the score of 

 expense, with that agent as a means of propelling machinery, but 

 that it might be used in some cases in which expense of power was 

 not a consideration to be weighed against the value of certain 

 objects to be attained. A great amount of labor has since been 

 devoted to this invention, especially at the expense of the Govern- 

 ment of the United States, by the late Dr. CHARLES G. PAGE, but 

 it still remains in nearly the same condition it was left in by my- 

 self in 1831. 



I also applied, while in Albany, the results of my experiments 

 to the invention of the first electro-magnetic telegraph, in which 

 signals were transmitted by exciting an electro-magnet at a distance, 

 by which means dots might be made on paper, and bells were struck 

 in succession, indicating letters of the alphabet. 



In the midst of these investigations I was called to Princeton, 

 through the nomination of Dr. JACOB GREEN, then of Philadel- 

 phia, and Dr. JOHN TORREY, of New York. 



I arrived in Princeton in November, 1832, and as soon as I 

 became fully settled in the chair which I occupied, I recommenced 

 my investigations, constructed a still more powerful electro-magnet 

 than I had made before one which would sustain over three 

 thousand pounds, and with it illustrated to my class the manner 



