280 HENRY AND THE TELEGRAPH. 



icists in this special departmeut, careful experiment only tended to show 

 " the imi)racticability of the scheme." 



It is at this point that there appears a new explorer in the electro- 

 magnetic field; a field from which apparently all the laurels had been 

 already gathered. Joseph Henry, elected to the professorship of mathe- 

 matics and natural philosophy in the Albany Academy, of New Yorlc, in 

 1826, commenced very shortly afterward his scientific investigations. 

 Sturgeon, in 1824, had pointed out the proper manner of making an 

 "electro -magnet," and had also greatly improved lecture-room apparatus 

 for illustrating the torsional reaction between a permanent magnet and 

 a galvanic circuit when either is made movable. By introducing in 

 such cases a larger and more powerful magnet he had succeeded in ex- 

 hibiting the usual phenomena on a larger scale with a considerable re- 

 duction of the battery xDOwer.* 



Henry was enabled by his skillful experimental investigations to ex- 

 hibit all the class illustrations attempted by Sturgeon, not only on a 

 still larger and more conspicuous scale, with the use of feeble magnets 

 (where required), but with a still further reduction of the battery power. 

 And he moreover carried out the same results to other cases where an 

 artificial magnet is inapplicable, as for example, in the illustration of 

 Ampere's fine discovery of the mutual action of two electric currents on 

 each other, or of the influence of the terrestrial magnetism on a current, 

 as in Ampere's swinging galvanic ring, or the floating ring of De La 

 Eive. These very 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 sensibility of the galvanometer. 



The coils employed by Henry in the various articles of apparatus thus 

 improved, comprised usually about twenty turns of fine copper wire 

 wound with silk to prevent metallic contact, the whole being closely 

 bound together. To exhibit for instance Ampere's ingenious and deli- 

 cate experiment showing the directive action of the earth as a magnet 

 on a galvanic current when its conductor is free to move, (usually a small 

 wire frame or ring, of a few inches in diameter, with its extremities dip- 

 ping either into mercury cups or into mercury channels,) the effect was 

 strikingly enhanced by Henry's method of suspending by a silk thread 

 a large circular coil, 20 inches in diameter, of many wire circuits bound 

 together with ribbon, — the extremities of the wire protruding at the 

 lower part of the hoop, and soldered to a pair of small galvanic plates; — 

 when by siinpl^^ placing atumblerof acidulated water beneath, the hoop 



* Transaciions of the Society for the cuconrar/ement of Arts, etc. 1825, vol. xliii, pp. 38-52. 

 Sturgeon's battery (of a single element) consisted " of two lixed hollow concentric cyl- 

 inders of thin copper, having a movable cylinder of zinc placed between them. IliS 

 superficial area is only 130 square inches, and it weighs no more than I lb. 5 oz." Mr. 

 Stui'geon was deservedly awarded the silver medal of the Society for the Encourage- 

 ment of Arts, &c. " for his improved electro-magnetic apparatus." The same is de- 

 scribed also, in the Annals of Philosophy, Nov. 1826, vol. xii, n. s. pp. 357-3'JI. 



