58 MEMORIAL ol JOSEPH HENRY. 



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

 ning <>f the ensuing year, January, L831, in that notable firsl 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. 



v ii RGEOM may he said to have first made an electro-magnet; 

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

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

 electric telegraph to a lone- 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. lie also 

 showed what kind of battery must be employed to project the 

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

 siiould surround the magnet used to receive this current and to 

 do the work.* 



'The following appear t'> be tin- main points in the order of discovery which 

 l.-il tn ill.- electro-magnetic telegraph. Thej are here condensed from Professor 

 Henry's "Statement," in tin- " I *i-« ..-.*■. 1 1 1 1 1_: ^ "1" the Regents," published in the 

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

 u. Taylor t<> his "Memoir of Joseph Henry and his Scientific Work," read 

 before the Philosophical Society of Washington : 

 ism 1S20. Oersted showed that a magnetic needle is deflected by the action of a 



current "i galvanic electricity passing near ii. It recently appears that this 



discovers hail already been made as early as tin- year 1802, by Romagnesi, 



ami published in ISO.'). 

 1820. Ai; \<.ii discovered that while a galvanic current is passing through a copper 



win' it is capable of developing magnetism in soft iron. 



