278 HENRY AND THE TELEGRAPH. 



marvelous progeny. In the ^anie year, 1820, Dominique Francois Arago, 

 of Paris, announced, "On repeating the experiments of the Danish 

 physicist, I have observed that the same current will develop strongly 

 in strips of iron or steel, the magnetic power. . . . The conjunctive 

 wire communicates to soft iron but a momentary magnetization ; but to 

 small pieces of steel it gives frequently a permanent magnetism. I have 

 been able thus to completely magnetize sewing-needles."* 



This germ of a new i)ower required, as usual, the successive labors of 

 more than one philosophic investigator to develop fully its caj^acities. 

 To William Sturgeon, of Woolwich, England, belongs the distinguished 

 honor (too little appreciated by his countrymen) of giving to the scien- 

 tific toy of Arago a suitable form, and thus of first i)rodncing in 1824, the 

 true electro-magnet with its intermittent control of an armature. Dis- 

 pensing with the glass tube of Arago, Sturgeon constructed a horse-shoe 

 bar of soft iron (after the form of the usual permanent magnet), which he 

 coated with a non-conducting resinous varnish. Then wmding a copper 

 wire in a loose coil directly about the limbs of the horse-shoe, on brmg- 

 ing the ends of the wire in connection with the poles of a single galvanic 

 pair of moderate size, he found his temporary magnet capable of sus- 

 taining several i^ounds by its armature; and on breaking the circuit, 

 becoming instantly powerless. 



It resulted from the correlative function of the galvanic current in 

 directing transversely a x^ermanently magnetized needle (first discovered 

 by Eomagnosiand Oersted), or in inducing temporary magnetism hi iron 

 thus transversely placed (first discovered by Arago and Sturgeon), that 

 two distinct methods of signaling were offered by this new agency, 

 accordiiigly as a i^ermanent or a temporary magnet were employed. In 

 the former case, the determined oscillations of the magnetic har, by 

 means of intermittent currents in a surrounding coil, would form the 

 indicating device ; and in the latter case, the determined oscillations of 

 the armature, by means of intermittent currents in the coil surrounding 

 its associated magnet, would give the indication. Hence the two types 

 of electro-magnetic telegraph; the magnetic -needle system, and the 

 magnetic-armature system, t 



On experimenting with the galvanometer needle, it was very soon dis- 

 covered that it responded only to variations of surface action in a single 

 pair of galvanic elements, and that a large number of galvanic cells (as 

 in the Cruickshanks battery), having even a greater total surface of oxi- 



* Annalei< de Chimie et de Physique, 1820, vol. xv, pp. 93, 95, Arago's method of experi- 

 mentatiou cousisted in ^Yilldill.£|;thc wire conuectiug tlie poles of the battery, around a 

 glasw tube iu a loose helix, within which tube small pieces of iron or steel were placed. 

 Sir Humphrey Davy, of England, not long afterward, also magnetized steel-needles 

 by galvanism ; and even effected the result with ordinary electricity from a Leydeu-jar 

 battery. (Annals of PhUosopli}!, August, 1821, vol. ii, n. s. pp. 81-88.) This was the 

 gerui — though scarcely more than the germ — of the electro-magnet. For a notice of 

 early anticipations of electro-magnetism, see " Supplement,"' Note C. 



t A modiiication of the latter system, by which the oscillations of an armature are 

 superseded by the variable attraction between the magnetized core and its hollow 

 galvanic coil, might perhaps be considered as forming a third type — that of the 

 "axial" uuxgnet. This has been employed in House's printing telegraph. 



