HENRY AND THE TELEGEAPH. 273 



netic needle, was observed and announced b;v »^ Italian savant, Gian 

 ]3onienico Eomagnosi, of Trent, at the beginning of the present cen- 

 tury, (shortly after the production of the galvanic battery by Volta,) 

 this important phenomenon attracted no attention, and produced no re- 

 sults, uutil it was republished two decades later by the Danish physicist.* 

 In the same year — almost immediately after Oersted's announcement, 

 Prof. Johaun S. C. Schweigger, of Halle, made a great improvement on 

 his galvano-magnetic indicator (of a single wire circuit), by giving the 

 insulated wire a number of turns around an elongated frame longitudi- 

 nally inclosing the compass-needle, and by thus multiplying the effect of 

 the galvanic circuits upon the sensibility of the needle converted it into 

 a real measuring instrument, — a '' galvanometer."t 



This delicate indicator at once suggested a new mode of galvanic tele- 

 graphing. In a memoir read to the '^ Royal Academy of Sciences," at 

 Paris, October 2, 1820, Andre Marie Ampere, affirming " the possibility 

 of deflecting a magnetic needle at a great distance from the pile, through 

 a very long conducting wire," remarked : " This exj^eriment, suggested 

 to me by the illustrious Laj^lace, was completely successful. . . . 

 From the success of the experiment " he added, " it is feasible by means 

 of as many conducting wires and magnetic needles as there are letters, 

 (each letter being assigned to a separate needle,) and by help of a bat- 

 tery at a distance, with its poles alternately connected with the extrem- 

 ities of each conductor, to establish a kind of telegraph adapted to 

 transmit over intervening obstacles whatever information may be de- 

 sired to the person observing the letters of the needles. A set of keys 

 near the battery, bearing corresponding letters and making connection 

 by their depression, would offer a facile means of correspondence ; re- 



*As early as 1802, eighteen years before Oersted's discovery, M. Eomagnosi, a publi- 

 cist and physicist of Trent, observed the detlectiou of the magnetic" needle when 

 placed near a parallel conductor of the galvanic current. An account of this dis- 

 covery was published in the Gaszetta cli Trcnto, August 3, 1802. See "Supplement," 

 Note B. 



t " Additions to Oersted's Electro-magnetic Experiments," a memoir read at the Xatur- 

 forschenden Gesellschaft at Halle, September Ifi and November 4, 18-20. An abstract of 

 this paper was published in the Alh/emeine Litcratur-Zcifung of Halle, (4to,) November, 

 1820, No. 296, vol. iii, col. 621-624. The full memoir ajipeared in the Joiinial filr 

 Chemieund Physik, 1821, vol. xxxi, pp. 1-17; and "Additional Eemarks," etc. by Dr. 

 Schweigger, in the same volume, pp. 35-41. 



A galvanometer of somewhat ditterent form, having a vertical helix and employiuo- 

 an unmagnetized needle, was very shortly afterward independently devised by Johanu 

 Christian Poggendortf, of Berlin; and as he preceded Schweigger in publishing an ac- 

 count of it, he is sometimes regarded as the original inventor. {Jidinhnrf/h I'hlUmophi- 

 cal Journal, July, 1821, vol. v, p. 113.) Schweigger designated his device' an " Electro- 

 magnetic Multiplicator " ; Poggendortf designated his arrangement a " Galvano-mag- 

 netic Condensator." Professor Oersted remarks, " lumicdiately after the discovery of 

 electro-magnetism, M. Schweigger, professor at Halle, invented an apparatus admirably 

 adapted for exhibiting by means of the uuignetic needle, the feeblest electric currents. 

 M. Poggendorff, a distinguished young savant of Berlin, constructed an 

 electro-magnetic multi])lier very shortly after M. Scliweigger, with which he made 

 some striking experiments. M. Poggendortl's work having been cited in a book on 

 electro-magnetism by the celebrated M. Ernan, (published'iujniediately after the dis- 

 covery of these phenomena,) became known to several i)hilosoi>hers before that of M. 

 Schweigger." (Annales dc Chimic et dc PlujaUnw, 1823, vol. xxii, pp. 358-360.) 



S. Mis. 59 18 



