24 



■wire must be employed to receive and multiply the effect of the current 

 enfeebled by its transmission through the long conductor. In the local 

 or short circuit either an intensity or a quantity magnet may be era- 

 ployed. If the first be used, then with it a compound battery will be 

 required ; and, therefore, on account of the increased resistance due to 

 the greater quantity of acid, a less amount of work will be performed by 

 a given amount of material ; and, consequently, though this arrangement 

 is practicable it is by no means economical. In my original paper I 

 state that the advantages of a greater conducting power, from using 

 several 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 effect 

 Avould be less. In accordance 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 customary to employ a battery of one or two ele- 

 ments with a much thicker wire and fewer turns. 



It Avill, 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 which I made. Arago and Sturgeon, 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, 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 telegraph when, in my paper, 

 I stated 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-m;ig- 

 netism, and the other the transmission of or calling into action power at 

 a distance. The first was carried into execution in the construction ot 



