I8d 



influence is praetieall}' not existing. Witli regard to the crystalline 

 form the equilibrium of these orvstals is indifferent. 



C. For our special model the whole still unused store of energy 

 may be comprised in the one expression 



EkLs 



with which the surface energy of the crystal corresponds in the three 

 dimensional case; by the side of this there is left nothing that could 

 answer to an energy of angular points or sides in the three- 

 dimensional case, with which Bkilloi'in, Veknadsky and Pawlow') 

 work. Now however the model can be made more general by 

 making e. g. moreover those isotropic attractive forces act between 

 the molecules, with which Laplace, Gauss, and van der Waals work 

 with action spheres, which still contain many molecules' ). It remains 

 noteworthy that then actually special side and angular point energies 

 ap|)car, whose numerical value remains undetermined for the present '). 



D. We have for the pi'esent not entered any further into the 

 molecular interpretation of the cleavage directions. More recent views 

 on this head are found in a study of P. P. Ewald") on the structure 

 of diamond. It would be interesting to ascertain whether one has 

 also as a rule to do with vicinal planes of the ideal cleavage planes 

 in the cleavage process. For the rest it would not be sufficient for 

 a complete analysis of the cleavage process to ascertain what cleavage 

 planes break a minimum of bindings; also the elastic deformation 

 preceding the cleaving is in principle a factor to determine the orien- 

 tation of the cleavage planes. 



') See tlie citations § 1. 



-) In this connection it may be mentioned that Einstein Ann. d. Phys. 34 (1911) 

 p. 165, comes to llie conclusion from the law of Eötvüs that also in liquids an 

 attraction may be assumed only between those neighbouring molecules that are 

 in immediate contact. 



') In the current derivation of the fundamental equations of the capillarity the 

 terms in question vanish, because in a certain point of the derivation the assump- 

 tion is made use of that the curvature rays of the surface remain everywhere 

 above a definite finite value. Gf. among others H. Minkowski, Art. Kapillaritat, 

 Math. Encykl. V. 9, § 14, transition between equation (24) and (26). First of all 

 this supposition does not hold for crystal sides and angles, but moreover also 

 e.g. at the side in which three liquids are in contact with each other. Brillouin, 

 Ann Ghim. et Phys. [7] 6 (1895) p. 540 has demonstrated that the structure of 

 the groove which is formed when glass and other substances are scratched is 

 chiefly determined by the side and angular point energy. 



*) Ann. d. Phys. 44 (1914) p. 281. 



