Professor Joseph Henry's Invention 



is operated with a battery of from twelve to 

 twenty-four elements or more, while in the local 

 circuit it is customary to employ a battery of one 

 or two elements with a much thicker wire and 

 fewer turns. 



It will, I think, be evident to the impartial 

 reader that these were improvements in the elec- 

 tro-magnet, which first rendered it adequate to 

 the transmission of mechanical power to a dis- 

 tance ; and had I omitted all allusion to the tele- 

 graph in my paper, the conscientious historian of 

 science would have awarded me some credit, 

 however small might have been the advance 

 which I made. Arago and Sturgeon, in the ac- 

 counts of their experiments, make no mention of 

 the telegraph, and yet their names always have 

 been and will be associated with the invention. 

 I briefly, however, called attention to the fact 

 of the applicability of my experiments to the 

 construction of the telegraph; but not being 

 familiar with the history of the attempts made 

 in regard to this invention, I called it "Barlow's 

 project," while I ought to have stated that Mr. 

 Barlow's investigation merely tended to disprove 

 the possibility of a telegraph. 



I did not refer exclusively to the needle tele- 

 graph when, in my paper, I stated that the mag- 

 netic action of a current from a trough is at least 

 not sensibly diminished by passing through a long 

 wire. This is evident from the fact that the 

 immediate experiment from which this de- 

 duction was made was by means of an electro- 

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