ELECTRO-MAGNETISM. 



835 



Ism was before known to do ; that the magnetizing 

 power is exerted by electricity, whether procured by 

 a galvanic apparatus, or a common machine ; that 

 powerful magnets may be formed, by conducting 

 electric currents round steel wires, as in the helix, 

 and that the position of the north and south poles of 

 these magnets depends upon the direction in which 

 the currents are made to move round them. These, 

 and a great number of other facts, it is conceived, 

 clearly demonstrate the perfect resemblance, or 

 rather identity, of electricity and magnetism. Mag- 

 netic phenomena are thus, in fact, a series of elec- 

 trical phenomena ; and magnetism may, with pro- 

 priety, form a branch of electricity, under the head of 

 Electrical Currents. Though this intimate relation or 

 identity be admitted, it is not so obvious how, by it, 

 the properties of 'the common magnet are explained. 

 Currents of electricity, according to the theory, 

 are essential to the production of magnetic pheno- 

 mena ; but these are not obvious in a common magnet. 

 M. Ampere has suggested their existence, however, 

 and has so arranged them theoretically, as to account 

 for a great proportion of magnetic appearances A 

 magnet he conceives to be an assemblage of as many 

 electric currents, moving round it in planes perpen- 

 dicular to its axis, as there may be imagined lines, 

 which, without cutting one another, form closed 

 curves round it. Magnetization, he says, is an 

 operation by which there is given to the particles of 

 steel (which, of the more common metals, appears to 

 be the only one capable of being permanently impress- 

 ed with this power) an electro-motive energy, which 

 causes a circulation of these currents to be continued 

 round them. The excitation and continuance of this 

 electro-motive action is rendered less improbable, 

 when we consider the electric power developed in 

 the tourmaline and boracite by heat alone, and when 

 we find, as in the electrical columns of De Luc and 

 Zamboni, that electricity may be generated for years 

 without ceasing or diminishing, by a small and simple 

 apparatus. Such, then, is the constitution of a mag- 

 net. It is a mass of iron or steel, round the axis of 

 which electric currents are constantly circulating, 

 and these currents attract all other electric currents 

 flowing in th same direction, and repel all others 

 which are moving in an opposite direction. 

 From these attractions and repulsions another effect 

 follows, that the currents of one magnet have always 

 a tendency to move any other magnet near it, till the 

 currents in the second shall coincide in direction with 

 those of the first. It is from this cause, as will pre- 

 sently be explained, that the magnetic needle always 

 turns to the meridian, and that the needle in Oersted's 

 experiments became at right angles to the connecting 

 wire. One important circumstance is always to be 

 kept in view, that the electric currents flow round 

 every magnet in the same direction in reference to its 

 poles. If, for instance, we place a magnet with its 

 north pole pointing to the north, in the usual posi- 

 tion of the magnetic needle, the current of electricity 

 flows round it from west to east ; or, on the eastern 

 side of the magnet, it is moving downwards, and on 

 the western side upwards ; on the upper side, from 

 west to east, and on the lower side, from east to west. 

 This, it is found, is a uniform law. On these princi- 

 ples the phenomena of magnetism are easily accounted 

 for. Thus, to take one of the most obvious and well 

 known facts, that of two magnets attracting when 

 their opposite poles are approached to one another, 

 as the north of one to the south pole of the other. 

 Let us suppose a magnet in the position which has 

 just been stated, with its north pole directed to the 

 north ; and let a second magnet be placed beyond 

 it, and in a line with it, with its north pole also pointed 

 to the r.rth. Then, it is obvious tliat the south pole 



of the second magnet will be next to the north pole 

 of the first ; and from their position it follows, that 

 the electric currents must be flowing in the same 

 direction, or, in both of them, from west to east : 

 hence, as currents moving in the same direction 

 attract, these opposite poles, if within a certain dis- 

 tance, ought to attract each other, whicii, accord- 

 ingly, will be found to be the case. Now, let the 

 second magnet be reversed ; let its south pole be 

 directed to the north, and its north pole approached 

 to the north pole of the first magnet ; the electric 

 currents will flow round the magnet in the same man- 

 ner as before ; but in reference to the. first magnet 

 and to the meridian, their direction will be reversed : 

 their direction will now be from east to west, upwards 

 on the eastern side, and downwards on the western ; 

 consequently, the currents in the two magnets, being- 

 now opposite, will repel, or the two north poles will 

 repel each other. 



In the experiments of professor Oersted, it was 

 found, as has been stated, that when the extraneous 

 influence of the magnetism of the earth was counter- 

 balanced, the tendency of a magnetic needle always 

 was to place itself at right angles to the wire con- 

 necting the poles of the galvanic battery. The reason 

 of this is easily explained upon the present hypothesis. 

 In the needle, the currents flow round its axis from 

 end to end ; but in the connecting wire there is no 

 circulation round the axis, but a constant stream from 

 one end, namely, .the negative, to the other, the posi- 

 tive extremity: hence, for the current along the wire 

 to coincide .with the current across and round the 

 magnet, it is necessary that the latter shall stand 

 across the former ; and as it appears, that, from the 

 attractions and repulsions which these electric cur- 

 rents exert, they are able to move one or both of the 

 magnetic bodies (according as they are light and 

 mobile), till they coincide, the needle moves if the 

 wire is fixed till it stands at right angles to the wire; 

 and if the magnet is fixed, and the wire movable, 

 the reverse liappens. The other phenomena, of the 

 needle turning to the west when placed below the 

 wire, to the east when placed above it, &c., may 

 with facility be explained in the same manner by the 

 principles, that currents flowing in the same direction 

 attract ; and that in every magnet they move in a 

 constant current, which is, when the north pole is 

 turned to the north, from west to east, or upwards 

 on the west side, and downwards on the east side. 



The development of permanent magnetism in 

 steel needles when placed across the wire, while it 

 is only temporary when they are fastened parallel 

 with it, depends on the same cause : in the latter 

 case, it arises merely from the transmission of elec- 

 tricity from end to end, while, in the former, the elec- 

 tro-motive energy of the particles is developed and 

 called into action, which, when set in motion, seems 

 to have the power of continuing itself. These elec- 

 tric currents liave the power, which accumulated 

 electricity has not, of penetrating all substances, as 

 was before known respecting magnetism. This is 

 probably owing to their low state of tension ; and, in 

 conformity with this, large plates, which evolve elec- 

 tricity in but a slight intensity, produce magnetic 

 effects most distinctly. The agency of galvanism, 

 and that of common electricity, are equally capable 

 of giving rise to magnetism when flowing in currents, 

 which adds another to the proof that these are the 

 same power. 



To complete the view of Ampere's doctrine, it re- 

 mains only to explain the influence of the earth on 

 the magnet, by which the needle is kept always in 

 one position, nearly coinciding with the meridian. 

 He asserts, that currents of electricity, analogous to 

 those whicii circulate round every magnet, are coil- 



