210 Prof. J. A. Ewing on the Molecular 



regular hexagon, with one in the middle, have a great variety 

 of possible stable configurations, of which these are examples: — 



Fig. 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 that there is stability for small displace- 

 ments, but different positions of the group may be stable in dif- 

 ferent degrees, and if members of the group be turned through 

 a sufficiently great angle, they become unstable, and fall into a 

 new position of stability, bringing about a partial reconstruc- 

 tion of the lines that characterize the group. Special interest 

 attaches to square patterns, from the fact that iron and nickel 

 (probably cobalt also) crystallize in the cubic system. In a 

 square pattern of many members, we find, in general, lines 

 running parallel with all sides of the square when the group 

 settles without directive force after a disturbance. 



Let the group, or collection of groups, be subjected to an 

 external magnetic force, .f), gradually increasing from zero. 

 The first effect is to produce a stable deflexion of all members 

 except those which lie exactly along or opposite to the 

 direction of <£)• This results in giving a small resultant 

 moment to the group (assuming that there was none to begin 

 with) , which increases at a uniform or very nearly uniform 

 rate as »£) increases. This corresponds to the first stage in 

 the magnetization of iron or other magnetic metal (a, fig. 3). 

 The initial susceptibility is a small finite quantity, and it is 

 sensibly uniform for very small values of .jj. 



Suppose that, without going beyond this stage, we remove 

 «£) ; the molecular magnets, not having been deflected beyond 

 the limit of stability, simply return to their initial places, and 

 there is no residual magnetism. This, again, agrees with the fact 

 that no residual magnetism is produced by very feeble mag- 

 netizing forces. Up to this point there has been no magnetic 

 hysteresis. But let the value of ,Q be increased until any 



