ESSAYS 509 



In all these cases one must of course take into account the stresses due to the 

 charges themselves and the strain effects due to the temperature change 

 accompanying the passage of a current, but it seems very doubtful if these are 

 adequate to explain the results. 



Not the least powerful argument in favour of an electrical basis for cohesion is 

 the principle of economy. Unless such an hypothesis is admitted, the existence 

 of an absolutely new and unrelated form of energy must be postulated, or at the 

 least it must be supposed that Newton's law ceases to be true for minute distances, 

 thus making cohesive tractation a special case of gravitation. 



Still another line of thought is suggested by crystal formation. It is in- 

 conceivable that the links which bind molecule to molecule in crystal architecture 

 can essentially differ from those which bind atom to atom in molecular and sub- 

 crystalline structure. As has been observed by Griineisen in the case of crystal 

 formation, cohesive forces are vectorised, and this is a perfectly logical result to 

 follow from the tractation of polarised stray fields, whereas if cohesion is simply a 

 tractation due to unknown causes and a pellation due to internal kinetic energy, 

 a polarised external effect is most difficult to conceive. 



