324 HENRY AND THE TELEGRAPH. 



GENERAL SU3IMARY. 



From the foregoing partial history of the origiu and development of 

 the electro-magnetic telegraph, it is sufQciently demonstrated that its 

 successful introduction has been effected by a considerable number of 

 independent contributions. The leading preparatory investigations and 

 discoveiies which opened the way for the telegraph, (though with no 

 such utilitarian end in view,) may be held to be : 



1st: The discovery of galvanic electricity by Galvani (1786-1790). 



2d: The galvanic or voltaic battery by Volta (1800). 



3d : The directive inlluence of the galvanic current on a magnetic 

 needle by Eomagnosi (1802), and by Oersted (1820). 



4th : The galvanometer by Schweigger (1820), the parent of the needle 

 system. 



5tli : The electro-magnet by Arago and Sturgeon (1820-1825), the par- 

 ent of the magnet system. 



Passing these, the next most imi)ortant series of steps in the evolu- 

 tion of onr present system of telegraphy, and having a more or less con- 

 scious reference thereto, are : 



First, and most vital: Henry's discovery in 1829, and 1830, of the "in- 

 tensity" or spool-wound magnet, and its intimate relation to the "inten- 

 sity " battery ; whereby its excitation could be efl'ected to a great distance 

 through a very long conducting-wire.* 



Second : Gauss's improvement in 1833, (or probably Schilling's improve- 

 ment considerably earlier,) of reducing the electric conductors to a single 

 circuit, by the ingenious aj^plication of a dual sign so combined as to 

 produce a true alphabet, t 



Third: Weber's discovery in 1833, that the conducting wires of an 

 electric telegraph could be efficiently carried through the air, without 

 any insulation except at their points of support. 



Fourtli: As a valuable adjunct to telegraphy, Daniell's invention of a 

 "constant" galvanic battery in 1830. 



Fifth : Steinheil's remarkable discovery in 1837, that the earth may 

 form the returning half of a closed galvanic circuit, so that a shigle con- 

 ducting-wire is sufQ(;ient for all telegraphic purposes. 



Sixth: Morse's adaptation of the armature of a Henry electro-magnet 

 as a recording instrument in 1837,| and in connection therewith the im- 



*Subor(liiiat('(l to this important step, the use of the armature as the signaling de- 

 vice and the tirst adoption of an acoustic signal might be mentioned. If Morse's 

 "relay" be judged by any as of snflicient importance to rank with the more essential 

 elements, then Henry's earlier and still more important device of the terminal short 

 circuit magnet of "(juantity" mnst not be overlooked. 



tThe probable anticipations of this, — by Lomond in 1787, by Cavallo in 179r), and by 

 Dyar in l&[>, — are here neglected, as neither sntliciently delinite, nor as perhaps prac- 

 tically inllnential on the juogress of telegraphy ; though this recurrence of idea should 

 certainly not be lost sight of in any history of the origins of inveutious. 



t Reptend)er of 18;j7 is fixed upon as the earliest date on ^vhich an actual register of 

 intolligiltle signs was made by Professor Morse. (Now York Journal of Commerce, Sep- 

 tember 7, 18:)7.) These signs were not alphahctical, but were zig-zag markings rejire- 

 Bentiug numerals. 



