LETTER OF J. HENRY TO REV. S. B. DOD. 151 



application to the telegraph, and to illustrate this by constructing a 

 working telegraph, and had I taken out a patent for my labors at 

 that time, Mr. Morse could have had no ground on which to found 

 his claim for a patent for his invention. To Mr. Morse however 

 great credit is due for his alphabet, and for his perseverance in 

 bringing the telegraph into practical use. 



II. My next investigation, after being settled at Princeton, was in 

 relation to electro-dynamic induction. Mr. Faraday had dis- 

 covered that when a current of galvanic electricity was passed 

 through a wire from a battery, a current in an opposite direction 

 was induced in a wire arranged parallel to this conductor. I dis- 

 covered that an induction of a similar kind took place in the 

 primary conducting wire itself, so that a current which, in its pas- 

 sage through a short wire conductor, would neither produce sparks 

 nor shocks, would, if the wire were sufficiently long, produce both 

 those phenomena. The effect was most strikingly exhibited when 

 the conductor was a flat ribbon, covered with silk, rolled into the 

 form of a helix. With this, brilliant deflagrations and other elec- 

 trical effects of high intensity were produced by means of a current 

 from a battery of low intensity, such as that of a single element. 



III. A series of investigations was afterwards made, which 

 resulted in producing inductive currents of different orders, having 

 different directions, made up of waves alternately in opposite direc- 

 tions. It was also discovered that a plate of metal of any kind, 

 introduced between two conductors, neutralized this induction, and 

 this effect was afterward found to result from a current in the plate 

 itself. It was afterward shown that a current of quantity was 

 capable of producing a current of intensity, and vice versa, a cur- 

 rent of intensity would produce one of quantity. 



IV. Another series of investigations, of a parallel character, was 

 made in regard to ordinary or frictional electricity. In the course 

 of these it was shown that electro-dynamic inductive action of 

 ordinary electricity was of a peculiar character, and that effects 

 could be produced by it at a remarkable distance. For example, if 

 a shock were sent through a wire on the outside of a building, 

 electrical effects could be exhibited in a parallel wire within the 

 building. As another illustration of this, it may be mentioned 



