858 



LORD KELVIN. 



what was wanted for octo-polar electric aeolotropy in a homogeneous 

 assemblage of single atoms. I now fîncl (§ 40 below) that quartets of 

 electrions wild rest stably in 

 equilibrium, under the in- 

 fluence of the mu tuai repul- 

 sion between electrion and 

 electrion and attraction be- 

 tween atom and electrion, in 

 an equilateral homogeneous 

 assemblage in the configura- 

 tion indicated in fig. 7. The 

 quartets of electrions are 

 supposée! to have their 

 eciges parallel to the six 



lines of symmetry of the 



J J Fig. 7. 



assemblage. The plane of 



the paper is supposed to be that of the centres of the seven atoms. 

 The central point in each circle represents a simple electrion which 

 is at distance r, according to the notation of § 20 above, from the 

 plane of the paper on the near side; and therefore the other three at 



the corners of an equilateral triangle at distance ^ r on the far side to 



o 



make the electric centre of gravity of the quartet coincide with the 

 centre of its atom. The radius of circle on which thèse three lie is 



——- r or "94 r. The diagram is drawn correctly to scale according to 



o 



the value '612 # given for r in the table of § 20, on the supposition 

 that the circles shown in the diagram represent the electric sphères of 

 the atoms in contact. 



§ 40. Imagine now the electrions of each quartet to be rigidly con- 

 nected with one another and given freedom only to rotate about an 

 axis perpendicular to the plane of the paper. To ail of them apply tor- 

 ques; turning the central quartet of the diagram slowly and keeping ail 

 the others at rest. It is clear that the first 60° of turning brings the 

 central quartet to a position of unstable equilibrium, and 60° more to 

 a position of stable equilibrium corresponding to the first position, 

 which we now see was stable when the others are ail held fixed. We are 

 now judging simply from the mutual actions between our central quartet 



