Origin of Molecular Attraction, 



663 



to AD. If we call the direction of AD axial and directions 

 at right angles lateral, we can say that a cube is electrized in 

 the same direction as its two nearest axial neighbours and 

 in a direction opposite to that of its four nearest lateral 

 neighbours. Each cube attracts its six nearest neighbours. 

 I believe that this constitutes the chief part of the solution 

 of the main problem of cohesion. Consider two cubes in 

 lateral relation and electrized in the same direction. They 

 will repel one another till they reach the position of minimum 

 potential energy when infinitely apart. But two cubes in 

 lateral relation electrized in opposite directions will attract 

 one another to the position of minimum potential energy 

 when they are in contact. For a relative position between 

 axial and lateral the force between two cubes vanishes. We 

 conclude, then, that the principle of minimum potential 

 energy in Nature acts so as to give such an arrangement 

 as is set forth schematically in the last figure. In cubical 

 crystals the scheme may be a still closer representation of 

 fact. In the case of an amorphous mixture of substances 

 whose molecules are of different size and shape, we can make 

 a diagram of the state of affairs, such as that here given. 

 Let AD and BC be two lines representing the prevailing- 

 direction of electrization. 

 They correspond with the 

 straight lines AD and 

 BC of fig. 2. They are 

 like lines of electric force. 

 Between them lie two 

 similar curved lines. 

 Then draw the system of 

 lines that cut these or- 

 thogonally like equi- 

 potential surface. These 

 two sets of lines divide 

 up the space into region> 

 corresponding with the 

 squares of fig. 2, each 

 region representing the 

 domain of a molecule. The arrow indicates the direction 

 of electrization of each molecule. Here we have the con- 

 ditions for cohesion in an amorphous substance, the figure 

 showing how in a body of finite size there may be no 

 prevailing direction of electrization. Here we are re- 

 minded of the theoretically infinite range of the force of 

 each molecule and its practical restriction almost to the 

 nearest neighbours. 



