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MAGNETISM. 



MAGNETISM, as was proved by the important discovery of 

 Faraday, will produce electricity, but with this condition, 

 that being in itself static, to produce a dynamic force, motion 

 must be superadded to it : without this it is, in fact, direc- 

 tive, not motive, altering the direction of other forces, but 

 not, in strictness, initiating them. It is difficult to convey a 

 definite notion of the force of magnetism, and of the mode in 

 which it affects other forces. The following illustration 

 may give a rude idea of magnetic polarity. Suppose a 

 number of wind-vanes, say of the shape of arrows, with the 

 spindles on which they revolve arranged in a row, but the 

 vanes pointing in various directions : a wind blowing from the 

 same point with an uniform velocity will instantly arrange 

 these vanes in a definite direction, the arrow-heads or narrow 

 parts pointing one way, the swallow-tails or broad parts 

 another. If they be delicately suspended on their spindles, a 

 very gentle breeze will so arrange them, and a very gentle 

 breeze will again deflect them ; or, if the wind cease, and they 

 have been originally subject to other forces, such as gravity 

 from unequal balancing, they will return to irregular posi- 

 tions, themselves creating a slight breeze by their return. 

 Such a state of things will represent the state of the molecules 

 of soft iron ; electricity acting on them not indeed in straight 

 lines, but in a definite direction produces a polar arrange- 

 ment, which they will lose as soon as the dynamic inducing 

 force is removed. 



Let us now suppose the vanes, instead of turning easily, to 

 be more stiffly fixed to the axes, so as to be turned with diffi- 

 culty : it will require a stronger wind to move them and 

 arrange them definitely ; but when so arranged, they will 

 retain their position ; and should a gentle breeze spring up in 



