AEPINUS ATOMIZED . 



853 



§ 31. Regretting much not to be able (for want of time) to inclucle 

 estimâtes of absolute magnitudes in the présent communication, Tendit 

 with applications of our hypothesis to the pyro-electricity and piezo- 

 electricity of crystals. A crystal is a homogeneons assemblage of bodies. 

 Conversely, a liomogeneous assemblage of bodies is not a crystal if the 

 distance between centres of nearest neighbours is a centimètre or more; 

 itis a crystal if the distance betweeu nearest neighbours is 10~ 8 of a cm. 

 or less. Pyro-electricity and piezo-electricity are developments of 

 vitreous and resinous electric forces sucli as would resuit from vitreous 

 and resinous electrifi cation on différent parts of the surface of a crystal, 

 produced respectively by change of température and by stress due to 

 balancing forces applied to the surfaces. 



§ 32. To see how such properties can or must exist in crystals com- 

 posed of our hypothetical atoms with electrions, consider first merely a 



Fig. 6. 



row of equal tetraelectrionic atoms in a straight line, each having its 

 quantum of four electrions within it. Kg. 6 shows a configuration of 

 stable equilibrium of the electrions not, however, truly to scale. The 

 sets of three dots indicate trios of electrions at the corners of equilateral 

 triangles, the middle dot in each row being alternately on the far side 

 and the near side of the plane of the paper, which contains the centres 

 of the atoms and the remaining electrion of each four. Let C l9 C, C , be 

 the centres of the atom A\, //, A'. An easy calculation shows that the 

 quartet of electrions within A, regarded for the moment as a group of 

 four material points rigidly connected, is attracted to the left with a 

 less force by A\ than to the right by A' (in making the calculation 

 remember that Ai attracts ail the electrions within A as if it were a 

 quantity e of vitreous electricity collectée! at Ci, and similarly in respect 

 to A'). There are corresjjonding smaller différences between the opposite 

 attractions of the more and more remote atoms on the two sides of A. 

 Let à dénote the excess of the sum of the rightwards of thèse attractions 



