238 BULLETIN OP THE 



" Mr. Sturgeon of Woolwich, who has been perhaps the 

 most successful in these improvements, has shown that a strong 

 galvanic power is not essentially necessary even to exhibit the 

 experiments on the largest scale. . . . Mr. Sturgeon's suite 

 of apparatus, though superior to any other as far as it goes, does 

 not however form a complete set : as indeed it is plain that his 

 principle of strong magnets cannot be introduced into every 

 article required, and particularly into those intended to e.xhil)it 

 the action of the earth's magnetism on a galvanic current, or the 

 operation of two conjunctive wires on each other. To form 

 therefore a set of instruments on a large scale that will illustrate 

 all the facts belonging to this science, with the least expense of 

 galvanism, evidently requires some additional modification of 

 apparatus, and particularly in those cases in which powerful 

 magnets cannot be applied. And such a modifi(!ation appears to 

 me to be obviously pointed out in the construction of Professor 

 Schweigger's Galvanic Multiplier : the principles of this instru- 

 ment being directly applicable to all the experiments in which 

 Mr. Sturgeon's improvement fails to be useful."* 



The coils employed 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 example Ampere's 

 ingenious and delicate experiment showing the directive action 

 of the earth as a magnet on a galvanic current when its con- 

 ductor is free to move, (usually a small wire frame with its 

 extremities dipping either into mercury cups, or into mercury 

 channels,) or its simpler modification, the " ring" of De La Rive 

 (usually an inch or two in diameter and made to freely float 

 with its galvanic element in its own bath,) the effect was 

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

 thread "a large circular coil twenty inches in diameter, of many 

 wire circuits bound together with ribbon, — the extremities of the 

 wire protrnding at the lower part of the hoop, and soldered to a 

 pair of small galvanic plates ;— when by simply placing a tumbler 

 of acidulated water beneath, the hoop at once assumed (with a 

 few oscillations) its equatorial position transverse to the mag- 

 netic meridian. By a similar arrangement of two circular coils 

 of different diameters, one suspended within the other. Ampere's 

 fine discovery of the mutual action of two electric currents on 

 each other, was as strikingly displayed. Such was the character 

 of demonstration by which the new Professor was accustomed to 

 make visible to his classes the principles of electro-magnetism : 

 and it is safe to say that in simplicity, distinctness, and efficiency, 

 such apparatus for the lecture-room was far superior to any of 

 the kind then existing. 



* Tra7is. Albany Institute, vol. i. pp. 22, 23. 

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