1857] WRITINGS OF JOSEPH HENRY. 433 



eral wires in the quantity magnet may in a less degree be 

 obtained by substituting for them one large wire; but in this 

 case, on account of the greater obliquity of the spires and 

 other causes, the magnetic efifect would be less. In accord- 

 ance with these principles, the receiving magnet, or that 

 which is introduced into the long circuit, consists of a horse- 

 shoe magnet surrounded with many hundred turns of a 

 single long wire, and is operated with a battery of from 12 

 to 24 elements or more, while in the local circuit it is cus- 

 tomary 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 electro-magnet which first 

 rendered it adequate to the transmission of mechanical 

 power to a distance; and had I omitted all allusion to the 

 telegraph in my paper, the conscientious historian of science 

 would have awarded me some credit, however small might 

 have been the advance that I had made. Arago, and Stur- 

 geon, in the accounts 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 called atten- 

 tion however to the fact of the applicability of my experi- 

 ments 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 telegraph when 

 I stated in my paper that "the magnetic 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 deduction was made, 

 was by means of an electro-magnet and not by means of a 

 needle galvanometer. 



At the conclusion of the series of experiments which I 

 described in Silliman's Journal, there were two applications 

 of the electro-magnet in my mind : one, the production of a 

 machine to be moved by electro-magnetism, and the other, 



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