MAGNETISM. 



Fig. 4. 



when the magnet is*- lifted up, they re- 

 main suspended in thick clusters. (Fig. 

 4, B.) A small number of filings are 

 also found adherent to the intermediate 

 parts of the bar, but they are evidently 

 attracted much more feebly than those 

 at the ends ; it may also be remarked 

 that there is a part of the magnet, gene- 

 rally mid-way between the two ends, to 

 which the filings have no tendency to 

 adhere at all, and which appears there- 

 fore to have no power of attraction. 

 Thus it appears that the attractive 

 forces, whatever be their nature, reside 

 chiefly at the poles. 



(11.) It is an established law of na- 

 ture, the knowledge of which we have 

 derived by induction from a vast variety 

 of phenomena occurring in every part 

 of the material universe, that all action 

 is attended by a corresponding reaction, 

 equal in degree, but opposite in its kind, 

 to the action itself. Mechanical philo- 

 sophy, in all its departments, abounds 

 with exemplifications of this funda- 

 mental principle ; many of these, indeed, 

 are matters of familiar observation. 

 The stretched rope pulls back with equal 

 force at both its ends ; the compressed 

 spring resists equally in two opposite 

 directions ; the exploding powder, at 

 the same moment that it propels the 

 ball, gives to the gun its recoil. In all 

 the effects resulting from cohesion, from 

 elasticity, from caloric, from animal 

 force, from gravitation, whether actuat- 

 ing the minutest particles of matter, or 

 the largest masses ; whether exerted on 

 the rolling waters of the ocean, or dis- 

 played on the grander scale of the pla- 

 netary movements, the same universal 

 law is rigidly observed. To every phy- 

 sical force there is opposed another and 

 a similar force. No material agent can 

 produce an effect upon another, without 

 being at the same time subjected to an 

 equal reaction from that other agent. 

 An attracting body must of necessity be 

 itself attracted, and a repelling body re- 

 pelled. This perfect reciprocity of ac- 

 tion takes place in all the agencies of 

 electricity; it exists also in those of 

 magnetism. 



(12.) If the two bodies exerting a 

 mutual action upon one another, be 

 very different in their size, the smaller 

 of the two will necessarily exhibit the 

 effects of this action more strongly than 

 the larger, because, its mass being less, 

 the same force will communicate to it a 

 greater velocity of motion. We find, 

 accordingly, that the small fragments of 

 iron in the experiment just described, 

 appear to fly towards the magnet, while 

 their reciprocal action on the magnet 

 itself is imperceptible. But this latter 

 action may be rendered sensible by try- 

 ing its effect on a magnet poised or sus- 

 pended in any of the ways above men- 

 tioned ; and we shall find that on pre- 

 senting a piece of soft iron to either of 

 the poles of the magnet, the latter is 

 slowly attracted by the iron. The at- 

 traction, therefore, between the magnet 

 and the iron is reciprocal. 



Let us next see what influence mag- 

 nets have upon one another. 



3. Attraction and Repulsion of Mag- 

 netic Iron. 



(13.) For the purpose of examining 

 the mutual action of two magnets, we 

 may either present to the poised magnet 

 another magnet held in the hand, or we 

 may place two poised magnets in dif- 

 ferent positions with respect to each 

 other. We shall find by sufficiently 

 varying these positions, that when the 

 poles of different magnets are brought 

 near one another, they in some cases 

 appear to be attracted towards each 

 other, while in others they manifest a 

 mutual repulsion. This, however, does 

 not happen capriciously ; for if we mark 

 the poles according to the distinction 

 already pointed out, we shall find that 

 two north poles always repel each other : 

 that two south poles also repel each 

 other : but that the north pole of one 

 magnet invariably attracts, and is of 

 course attracted by the south pole of 

 another magnet. 



(14.) It thus appears that there are 

 two species of magnetic powers, the 

 northern and the southern, which in 

 their mode of action are perfectly simi- 

 lar, but in their effects are directly op- 

 posite. 



(15.) Such of our readers as have 

 studied our Treatise on Electricity must 

 here be struck with the pointed analogy 

 which subsists between the phenomena 

 of magnetic attraction and repulsion, 

 and those of electricity. In both there 

 exists the same character of double 

 B 2 



