HENRY AND THE TELEGRAPH. 333 



"fonnd that a needle through which he had sent an electric shock had in consequenco 

 acquired a curious species oi" polarity; for instead of turning as usual to the north and 

 south, it assumed a position at right angles to this, its two ends pointing to the east 

 and west."* This curious phenomenon (which if properly investigated might have 

 led to the discovery of electro-magnetism) was exhibited by the action of common 

 frictional or mechanical electricity: galvanism not liaviug been discovered till some 

 time later. It was probably thi.s same transverse polarity that was afterward observed 

 by Mojon. * 



NOTED. (From p. 287.)' 



HENUY'S spool magnet in EUI50PE. 



Amonc the physicists of Europe who repeated Henry's experiments on a similar 

 scale, Claude S. M. Pouillet, professor of jjhysics at the lilcoU Poll/technique and director 

 of the Conserraioire at Paris, made in 1832, a magnet capable of sustaining 900 pounds. 

 At the session of the Societe Philomatique of Paris, for June 23, 1832, Pouillet gave an 

 account of recent experiments made by him with an electro-magnet of large size, 

 having several thousand feet of wire wound upon it. The following is the report of 

 this communication published in the "Bulletin" of the Society for August of that year: 



"M. Pouillet communicated to the Society the results of experiments which he had 

 just made on the magnetization of round bars of iron, (bent iu horseshoe form, and 

 surrounded on the arras with iron wire of a length of several thousand feet,) by 

 means of an electric current established in this iron wire. The magnetism thus ex- 

 cited in a magnet one foot in height, formed of a bar of iron two and a half inches iu 

 diameter, and wrapped with 4,000 feet of wire, is sufficiently strong to support a 

 weight up to 900 pounds, even when the contact of the armature with the magnet is 

 reduced to an edge: so that the magnetic force is in this case stronger than the molec- 

 ular attraction, t Attending such magnetization, on a connection being made be- 

 tween the two extremities of the conductiug wire, a spark and a strong shock are 

 produced. In another experiment, two similar magnets similarly arranged, having 

 been placed facing each other, and varied in distance from contact up to a separation 

 of a foot, the magnetization of the one produced a magnetization of the other by in- 

 duction ; so as to eifect an electric current and spark when the two extremities of the 

 conductiug wire were brought very close together. In the latter case there was felt 

 also a vivid shock. This shock may be communicated through a platinum wire even 

 to the distance of a hundred feet."t 



The source of this ' ' intensity " magnet is as unmistakable as is that of the magneto-elec- 

 tric spark obtainc<l by its means. Had the experimenter however divided his 4,000 feet 

 of wire into 50 or 60 separate coils, arranging suitably his galvanic battery in "multi- 

 ple arc" as a " quantity" battery, he would certainly have greatly increased the at- 

 tractive force of his magnet, and rendered it comiiarable to Henry's Yale-College mag- 

 net in lifting-power. 



Pouillet in the third edition of his Elements de Physique Experlmentale, published in 

 1837, gives a drawing of a double " intensity " magnet arranged like Henry's in a sup- 

 porting frame, of which he says: "Figures 432 and 433 represent an electro-magnet 



* P. M. Roget, Treatise on EUctro-mmjveiism, 1832, chap, i, art. 6, p. 3. (This treatise 

 is included iu the "Library of Useful Knowledge," vol. ii.) 



t [Notwithstanding the considerable range of distance through which magnetism 

 acts, it is not probable that the aggregate magnetic tenacity of iron iu any case 

 amounts to more than a very small fraction of its cohesive tenacity.] 



X Seance of 2od June, 1832. Kouveau Bulletin des Sciences, public par la " Soci6t6 Philo- 

 matique de Paris," livraison pour Aoilt, 1832, p. 127. This brief notice, republished in 

 Quetelet's Correspondance Malhematique et Phi/nique de I'Observatoire de Bruxelles, 1832, 

 liv. V, vol. vii, pp. 317, 318, is the only paper by Pouillet on the subject of magnetiza- 

 tion by electric currents, contained in the Catalogue of the Royal Society. Presumablj 

 therefore his only contribution on the subject. 



