126 The Smithsonian Institution 



trical science during the period of nearly thirty years which 

 had elapsed since this early experiment was made/ 



To strike signals upon a bell at the distance of 8000 feet 

 was a result accomplished in the same year in the commence- 

 ment hall of the Albany Academy. The importance of this 

 experiment in connection with the history of the telegraph is 

 discussed at greater length elsewhere. 



All these experiments were made in the autumn and early 

 winter of 1829 or 1830, as seems to be very clearly shown by 

 Miss Mary A. Henry in her recent essays.^ The fixing of 

 these dates is of considerable moment, since upon them de- 

 pend the dates of two other discoveries, that of self-induction 

 and that of magneto-electricity. 



The former, that of the so-called "extra current," made 

 August, 1829 or 1830, though it was not announced until 

 1832,^ is now conceded to him by all* and it was chiefly in 

 recognition of the discovery of self-induction that his name 

 was given to the standard unit of inductive resistance 

 at the International Congress of Electricians in Chicago, in 

 August, 1893, thus bestowing upon him, as Mendenhall ex- 

 presses it, " the high honor of a place in the galaxy of famous 

 physicists whose names shall be perpetuated in the metro- 

 logical nomenclature of all languages." At this congress, 

 composed of twenty-six representative men of science, from 

 nine great nations, Professor von Helmholtz presided. 



" It was gratifying to the American delegates in the 

 Chamber at Chicago," writes Mendenhall,^ " that the motion 



1 " Smithsonian Report," 1857, page 1 10. 3 A7tierkan Journal of Science, 1832, Vol- 



2 Henry, Mary A., "America's Part in the ume xxil, page 403. 



Discovery of Magneto-Electricity — A Study 4 This was, in 1834, rediscovered by Fara- 



of the Work of Faraday and Henry." I-V, day, who did not until some time after per- 



The Electrical Engineer, 1892, Volume xiil, ceive the relation of his work to that which 



page 27 et seq. "The Electro-Magnet; or had preceded. 



Joseph Henry's Place in the History of the 5 Mendenhall, T. C, "The Henry," At- 



Electro-Magnetic Telegraph," I-XII ; //'/(/., lantic Monthly, \o\\\m& i.xxill, pages 613- 



XVII, 1894, page I et seq. 614, No. 439, May, 1894. 



