1890.] Molecular Theory of Induced Magnetism. 



PIG. 7. 



CN being drawn normal to PP'. The restoring moment at first 

 increases with 0, but passes a maximnm at a value of which 

 depends on the relation of r to the distance between the centres. The 

 condition of equilibrium is 



pp7 



and as and 6 are increased the equilibrium becomes neutral, that is 

 to say, the condition of instability is reached, when 



f 



de 



sn 



(a-6) \ =* A ?L 8 ?5 



/ de> 3 ' 





These two equations serve to determine the value of and of 6 at 

 which instability occurs. If we have to deal with a long line of 

 magnets instead of a single pair, we have to write 2m 2 instead of m 2 

 in the restoring moment. 



A considerable amount of stable deflection is possible when the 

 distance between the poles is not small compared with r. When the 

 direction of is not much inclined to CC' (that is, when a has a 

 value approaching 0) there is no instability. In rows having various 

 inclinations to <>, the first to become unstable as is increased will 

 be that for which. is equal to ^v. 



