ESSAYS 



507 



Lateral stresses are due to the change of position of the molecules. Thus in 

 the case of tension the longitudinal pairs are separated, thus diminishing the 

 tractation at intermediate points. The pellation of laterally disposed molecules 

 displaces them towards the field of decreased pressure so that there is a general 

 lateral contraction. In the case of axial compression there is increased pellation 

 between the longitudinal pairs, and the lateral molecules are displaced into new 

 positions of equilibrium, thus giving a general sideward expansion. Poisson's 

 ratio indicates the manner in which the lateral forces are modified. 



In the absence of accurate knowledge as to the mechanical constitution of 

 molecules and atoms it is difficult to suggest a law for the pellation. Certainly it 

 depends on the temperature, and it seems probable that the kinetic energy of the 

 molecules is related to the gas constant, subject to certain deduction for the 

 potential involved in the change of tractation. The only step at present possible 

 seems to be to assume a law for the tractation from electrical and gravitational 

 analogies, and then deduce the repulsion from stress-strain effects by difference. 



E*cE*s op Attraction 

 ovett Repulsion 



£*cess or Repulsion 

 over Attraction 



Tension 



CortiPSCSStoh 



Stress Strain Diagram 



(Sum ©^Cohesion Diagrams) 



We have seen that tensile stress lies near in value to electrostatic force, but 

 the fact that the latter explains atomic linkage, whereas cohesion is only slightly 

 discriminatory, suggests that we cannot directly identify them. Abegg and Veles 

 hypothesis as to secondary valency does help to render consistent the formation of 

 homogeneous molecules, but something more is needed to explain the adhesion of 

 molecule to molecule, and the writer would add to it the idea that the electrical 

 fields which correspond to atomic linkage are not wholly neutralised. A " stray 

 field" can be conceived to exist which is capable of tractating other similar fields 

 with an intensity of say one-hundredth that of a nascent atom and shows as 

 gravitation for distances of more than a few molecular diameters. 



On this basis the writer has produced the following empirical formula, which 

 satisfies approximately the conditions required for cohesive tractation at smal 

 distances and gravitational force at large distances : 



_ Gm 1 



where / 2 is the tractation between two isolated molecules, 

 Newtonian constant for gravitation, 

 mass of a molecule, 

 molecular interval (centre to centre) 



„ „ at absolute zero. 



G 



m 

 d 



>» >j 



