ELECTRO-MAGNETISM. 



to the directions in which it is most pro- 

 ductive. The electricity thus perpetu- 

 ally in action does not appear to be in 

 any respect influenced by the presence 

 of the workmen and their candles ; nor 

 even by the explosions of gunpowder in 

 blasting. 



(335.) Mr. Fox observes that ores 

 which transmit electricity have generally 

 some conducting material interposed in 

 the veins between them and the surface : 

 a structure which appears to bear some 

 analogy to the ordinary galvanic combi- 

 nations. These electrical currents which 

 pervade mines were found to have vari- 

 ous and frequently opposite directions in 

 different parts of the same mine. 



(336.) The metals are probably not 

 the only substances capable of giving 

 rise to electrical currents in the earth ; 

 for it is well known that galvanic com- 

 binations may be formed by arrange- 

 ments of elements that are not metallic. 

 (See Galvanism, 87.) The direction 

 of each current will of course be deter- 

 mined by the relative positions of the 

 elements* from which it is derived ; but 

 even if we suppose the arrangement of 

 these elements to be fortuitous, a pre- 

 vailing current will still result, arising 

 from the difference of their actions ; for 

 it is infinitely improbable that, without a 

 designed arrangement, the currents in 

 opposite directions should be exactly 

 equal, so as to destroy one another. 

 Irregularities of distribution probably 

 exist with regard to the materials com- 

 posing the interior of the globe ; the 



resultant electro- magnetic action of the 

 whole combination being that of which 

 we witness the effects, and which may 

 be considered as due to electrical cur- 

 rents circulating in directions parallel 

 to the magnetic equator round the sur- 

 face of the earth. 



(337.) Even in the irregularities in- 

 cident to the magnetic forces derived 

 from the earth we may discern the 

 operation of causes which are periodical 

 in their operation. Thus the diurnal 

 and annual changes of the variation 

 of the needle may be traced to cor- 

 responding changes in the position of 

 the different parts of the earth with 

 regard to the sun, in as far as these 

 electric currents are dependent upon 

 solar influence. The progressive changes 

 in the variation, which embrace longer 

 periods of time, are less easily accounted 

 for, and appear referable to causes which 

 act at greater depths below the surface 

 of the earth ; and are probably connected 

 with chemical changes taking place in 

 the interior of the globe, of which we 

 can possess no certain knowledge. 



(338.) On the whole, then, it must be 

 allowed, that there are strong grounds 

 for the belief that there subsists some 

 mutual connexion, or rather an intimate 

 relation and affinity, between the several 

 imponderable agents, namely, Heat, 

 Light, Electricity, and Magnetism, 

 which pervade in so mysterious a man- 

 ner all the realms of space, and which 

 exert so powerful an influence over all 

 the phenomena of the universe. 



NOTE. Since the above was sent to the press, a paper, by Mr. Faraday, has been 

 communicated to the Royal Society, disclosing a most important principle in elec- 

 tro-magnetism, of which, I regret, I can only give the following brief statement. 



By a numerous series of experiments, Mr. Faraday has established the general 

 fact, that when a piece of metal is moved in any given direction, either in front of 

 a single magnetic pole, or between the opposite poles of a horse-shoe magnet, 

 electrical currents are developed in the metal, which pass in a direction at right 

 angles to that of its own motion. The application of this principle affords a com- 

 plete and satisfactory explanation of the phenomena observed by Arago, Herschel, 

 Babbage, and others, where magnetic action appears to be developed by mere 

 rotatory motion, and which have been erroneously ascribed to simple magnetic 

 induction, and to the time supposed to be required for the progress of that induc- 

 tion. The electro-magnetic effect of the elective current induced in a conductor 

 by a magnetic pole, in consequence of their relative motion, is such as tends con- 

 tinually to diminish that relative motion ; that is, to bring the moving bodies into 

 a state of relative rest : so that, if the one be made to revolve by an extraneous 

 force, the other will tend to revolve with it, in the same direction, and with the 

 same velocity. 



H2 



