Prof. J. A. Ewing. Contributions to the [June 19 r 



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 

 the opposite way. 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 configura- 

 tions 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 regular 

 hexagon, with one in the middle, have a great variety of possible 

 stable configurations, of which these are examples : 



2. 



Experimental study of the forms which may be assumed by 

 groups, and of the vibrations which may be transmitted through 

 groups, is interesting, but to pursue it would be beside my present 

 purpose. In all cases, the configuration assumed by a group is such 



