PHILOSOPHICAL SOCIETY OP WASHINGTON. 23t 



ing (Ersted's announcement of the torsional or equatorial reaction 

 between a galvanic conductor and a magnetic needle, had found 

 that a circulating galvanic current was capable not only of de- 

 flecting a suspended magnet, but of generating magnetism — per- 

 manently in sewing needles, and temporarily in pieces of iron 

 wire, when placed within a glass tube around which the conjunc- 

 tive wire of the battery had been wound in a loose helix; and had 

 thus created the "electro-magnet."* The scientific world was just 

 aroused to the close interrogation of this new marvel, each ques- 

 tioner eager to ascertain its most efficient conditions, and to in- 

 crease its manifestations. William Sturgeon of Woolwich, Eng- 

 land, had extended the discoveries of Ampere and Arago, by 

 dispensing with the glass tube, constructing a "horse-shoe" bar 

 of soft iron (after the form of the usual permanent magnet) coated 

 with a non-conducting substance, and winding the copper conjunc- 

 tive wire directly upon the horse-shoe ; and had thus produced the 

 first e^c^■e/^^ electro-magnet; — capable of sustaining several pounds 

 by its armature, when duly excited by the galvanic current. He 

 had also greatly improved lecture-room apparatus for illustrating 

 the electro-magnetic reactions of rotations, etc., (where a perma- 

 nent magnet is employed) by introducing stronger magnets, and 

 thereby succeeding in exhibiting the phenomena on" a larger 

 scale, with a considerable reduction of the battery power. f 



Faraday had not yet commenced the series of researches which 

 in after years so illumined his name, when Henry published his 

 firsrf; contribution to electrical science, in a communication read 

 before the Albany Institute, October 10th, 182T, "On some Modi- 

 fications of the Electro-Magnetic Apparatus." From his experi- 

 mental investigations he was enabled to exhibit all the class 

 illustrations attempted by Sturgeon, on even a still larger and 

 more conspicuous scale, with the employment of very weak magnets 

 (where required), and with a still further considerable reduction 

 of the battery power. These quite striking and unexpected results 

 were obtained by the simple expedient of adopting in every case 

 where single circuits had previously been used, the manifold coil 

 of fine wire which Schweigger had employed to increase the sen- 

 sibility of the galvanometer. He remarks : — 



magnet ; and appears? not to have been the first even to discover the 

 directive inflaenee of a current on a magnetic needle. 



■"' Annales de Chhuie et de Phijsiq're, 1820, vol. xv. pp. 93-100. 



t Trans, Soc. Encnuragement Arts, etc., 1825, vol. xliii, pp. 38-52. 

 This battery (of a single element) consisted " of two fixed hollow concen- 

 tric cylinders of thin copper, having a movable cylinder of zinc placed 

 between them. Its superficial area is only 130 square inches, and it 

 weighs no more than 1 lb. 5 ozs." Mr. Sturgeon was deservedly awarded 

 the Silver Medal of the Society for the Encouragement of Arts etc^, " for 

 his improved elect ro-maanetic apparatus." Described also in Thomson's 

 Annals of Philos., Nov. 1826, vol. xii., new series, pp. 357-3til. 



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