Theory of Induced Magnetism. 209 



to come to rest free from external magnetic force, they of 

 course assume a form which has no resultant magnetic moment, 

 provided the number be sufficiently great ; but it is apparent 

 that they do not arrange themselves in closed chains. Any 

 such configuration would in general be unstable. Many 

 stable configurations admit of being formed, and if the 

 magnets are again disturbed and left to settle, the chances are 

 much against any one configuration immediately repeating 

 itself. One general characteristic of these configurations is 

 that they contain lines consisting of two, three, or more 

 magnets, each member of a line being strongly controlled 

 by its next neighbours in that line, but little influenced by 

 neighbours which lie off the line on either side. Thus, if 

 there are two magnets simply, they form (as might be antici- 

 pated) a highly stable pair, thus : — 



With three magnets, two form a line along one side of the 

 triangle joining the fixed centres, and the third lies parallel, 

 or nearly so, facing oppositely. Four magnets will usually 

 form two lines with directions which lie nearly along two 

 sides of the quadrilateral ; but diagonally opposite magnets 

 may pair, leaving the others unattached. Suppose them set 

 at the corners of a rectangle with unequal sides, they may lie 

 in any of these forms 



if the inequality in distance be not too great. All these con- 

 figurations are stable, and the condition of least energy, while 

 making the first of them the most probable, does not prevent 

 the occasional formation of the others. In a long line, the 

 same condition leads in general to this formation : — 



but it is by no means uncommon to find a line broken into 

 two or more sections, thus : — 



Seven magnets grouped so that the centres of six form a 



