526 The Smithsonian Institution 



among intelligent people that the first commercially suc- 

 cessful electric telegraph line was 7iot erected in this country ; 

 that the telegraph can in no sense be called an American in- 

 vention, although the American system has proved to be so 

 superior that it has long ago practically superseded all others ; 

 and that by far the larger share of the credit for the success 

 of this system is due to Joseph Henry for his discovery of 

 the scientific principles upon which that success depended. 



In the mean time Henry was engaged in further researches 

 of the very highest importance. He sought to use the power- 

 ful magnets which he was now able to construct in the solu- 

 tion of a problem which had thus far baffled the efforts of the 

 ablest electricians in Europe. Having succeeded beyond all 

 others in producing niagnetisnt by using elechncity, he hoped 

 to be able to successfully attack the inverse problem, the 

 production of electricity from inagnetisfn. All ph}'sicists be- 

 lieved that this must be possible, but no one had hit upon 

 the method of doing it. Curiously enough, another great ex- 

 perimental philosopher, also a young man, had set for himself 

 the same problem and worked persistently upon it during 

 the month of August, 183 1. During the same month Henry 

 began a carefully-planned series of experiments, which, un- 

 fortunately, owing to his duties in the Academy, he was 

 obliged to give up, not being able to return to them for nearly 

 a year. Entirely ignorant of Henry's plans. Faraday, on the 

 30th of August, 1 83 1, — a memorable day in the history of 

 electricity, — made the capital discovery of induction, on which 

 practically all modern electrical development is based. En- 

 tirely ignorant of what Faraday had done, Henry again took 

 up the subject and had the good fortune to discover the iden- 

 tical phenomenon in another aspect, in which it is known as 

 self-induction. In the more recent advances in applied elec- 

 tricity, self-induction has come to be a matter of primary im- 



