ELECTRO-MAGNETISM. 



make five or six turns in the circle, and 

 then tying the coils together so as to 

 form a ring, which being thus composed 

 of a number of concentric circles, the 

 action of each is combined, and the power 

 as it were multiplied by the number of 

 turns. 



(97.) This difference in the effects 

 which the two sides of the plane of the 

 ring in this instrument have on the same 

 pole of a magnet, presents a very strik- 

 ing phenomenon, and exhibits a strong 

 analogy with the magnet itself. We 

 may in fact consider it as r; flat magnet, 

 having hYtwo poles in the centre of it, 

 two surfaces, the one on one side, and 

 the other on the other: so that if, on 

 looking at one of these surfaces, the 

 current is moving in the same direction 

 as the hands of a watch move when we 

 face the dial, then the side on which we 

 are looking may be regarded as having 

 the properties of the south pole; and 

 the other side that of the north pole. 

 The former attracts and is attracted by 

 the north pole of a magnet ; the latter 

 attracts and is attracted by the south 

 pole, and vice versa. 



(93.) A very curious phenomenon is 

 seen when a magnet is presented hori- 

 zontally to the vertical electro-magnetic 

 ring of M. De la Rive ; supposing the 

 mRgnet to be sufficiently slender to pass 

 easily through the ring. If the pole be 

 presented to it on the side where attrac- 

 tion takes place, the ring will move 

 towards it, till it arrives at the pole, and 

 then proceeds onwards in the same 

 course, the magnet being held in the 

 axis of the ring, till it reaches the middle 

 of the magnet ; but there it seems in- 

 clined to stop ; and then, after a few 

 oscillations, it settles, as in a position of 

 equilibrium: for if purposely displaced 

 by bringing it forwards towards the 

 other pole, it returns with a force which 

 shows that it is repelled from that other 

 pole. Let us now withdraw the magnet, 

 and turning it half round, so that its 

 poles are in directions the reverse of 

 what they were at first, and holding the 

 ring in one hand, let us again introduce 

 the magnet into it with the other hand, 

 until it is half-way through. Under 

 these circumstances it is just possible 

 that we may have brought it into such 

 a situation as that the ring may again 

 be in equilibrium, undetermined in what 

 direction to move; but the slightest 

 change in this position causes it to move 

 with an accelerated velocity towards 

 that pole which is nearest to it j and 



getting entirely clear of the magnet, it 

 is projected to a considerable distance 

 from it. At length, however, it stops, 

 and, gradually turning round, presents 

 the opposite face to the magnet ; attrac- 

 tion now takes place, and the ring re- 

 turns to the magnet with a force equal 

 to that with which it had before fled 

 from it ; and passing again over its pole, 

 finally rests in its position of equilibrium, 

 encircling the middle, or what may be 

 termed the equator of the magnet. In 

 the former position it was equally at- 

 tracted by the two poles of the magnet ; 

 in the latter it is equally repelled : and 

 accordingly the first was an unstable, 

 and the last a stable equilibrium. The 

 ring is represented in this last situation 

 injfig. 65, surrounding the middle of the 

 magnet, S, N. 



Fi. 65. 



(99.) M. De la Rive's apparatus may 

 be constructed so as not to require the 

 liquid in which it floats to consist of the 

 acid ; for if the copper plates be double, 

 and pass round the zinc plate, so as to 

 form a cell capable of holding the ncid 

 and the zinc plate, the whole combina 

 tion maybe enclosed in a glass cylinder, 

 which will enable it to float in water. 

 Both the surfaces of the zinc are thus 

 opposed to a surface of copper, as in the 

 construction proposed by Dr. \Vollaston. 

 (See Galvanism, $ 18.) This addition 

 was first suggested by Mr. Marsh, and 

 is represented in the preceding figure 

 (G">). The tube for this purpose, may 

 be made out of the neck of a Florence 

 flask. 



(100.) The magnetic properties of 

 circular conductors may be exhibited in 

 a striking manner by bending the wire 

 D2 



