58 MEMORIAL OF JOSEPH HENRY. 



cjarried on those investigations which, when published at the begin- 

 ning of the ensuing year, January, 1831, in that notable first paper 

 in the American Journal of Science and the Arts, at once brought 

 Henry's name to the front line among the discoverers in electro- 

 magnetism. 



Sturgeon may be said to have first made an electro-magnet; 

 Henry undoubtedly made the electro-magnet what it is. Just 

 after Barlow, in England, had declared that there could be no 

 electric telegraph to a long distance, Henry discovered that there 

 could be, how and why it could be; he declared publicly its practi- 

 cability, and illustrated it experimentally by setting up a telegraph 

 with such length of wire as he could conveniently command, 

 delivering signals at a distance by the sounding of a bell. 



Previously to his investigations the means of developing mag- 

 netism in soft iron were imperfectly understood (even though the 

 law from which they are now seen to flow had been. mathematically 

 worked out by Ohm), and the electro-magnet which then existed 

 was inapplicable to the transmission of power to a distance. Henry 

 first rendered it applicable to the transmission of mechanical power 

 to a distance; was the first actually to magnetize a piece of iron at 

 a distance, and by it to deliver telegraphic signals. He also 

 showed what kind of battery must be employed to project the 

 current through a great length of wire, and what kind of coil 

 should surround the magnet used to receive this current and to 

 do the work.* 



*The following appear to be the main points in the order of discovery wlilch 

 led to the electro-magnetic telegraph. They are here condensed from Professor 

 Henry's "Statement," in the "Proceedings of the Regents," publislied in the 

 Smithsonian Report for tiie year 1857, and from a note appended by Mr. William 

 B. Taylor to his "Memoir of Joseph Henry and his Scientific Work," read 

 before the Philosophical Society of Washington : 

 1819-1820. Oersted showed that a magnetic needle is deflected by the action of a 



ciuTcnt of galvanic electricity passing near It. It recently appears that this 



discovery had already boon made as early aa the year 1802, by IIomaonesi, 



and published In 1805. 

 1820. AuAoo discovered that while a galvanic current Is passing through a copper 



wire it la capable of developing magnetism in soft Iron. 



