Internal Pressure of a Liquid to its Dielectric Capacity. 115 



Probably the most correct view to take is that the orbit 

 (radius r) in the case of a given substance is constant, i. e. 

 is independent of temperature, pressure, and change of state, 

 whilst the rate o£ revolution of the valency electrons is not 

 thus constant, that is the angular momentum is not constant. 

 The possible variation in the angular momentum with tem- 

 perature and pressure should, however, be directly propor- 

 tional to the variation of the observed absorption or emission 

 frequencies with temperature and pressure. 



Returning now to the question of electromagnetic mole- 

 cular attractions due to revolving valency electrons of con- 

 stant orbit, since such attractions are exhibited by diamagnetic 

 substances it is necessary to assume that each molecule has 

 at least two valency electrons revolving in opposite directions. 

 There will thus be a tendency for the molecules to arrange 

 themselves into chains in which the electron revolving in a 

 given direction in one molecule approaches as closely as 

 possible to the electron undergoing similar motion in another. 

 Liquids may therefore not be so " structureless ,J as js usually 

 assumed*, and in this possibly is to be found the source of 

 optical activity exhibited by certain liquids. At the same 

 time, the kinetic energy of the molecules tends to break up 

 any regularity of arrangement, thereby diminishing; tho 

 molecular attraction if this be electromagnetic. In agree- 

 ment with this it is known that the cohesion diminishes as 

 temperature rises. This effect of temperature in modifying 

 the orientation of the molecules introduces virtually a factor 

 dependent upon temperature into the attraction expression, 

 so that the attraction is apparently less than that given by 



the inverse fourth power law, —% . In agreement with this, 



mention may be made of the empirical attraction term 



— 3 suggested by Dieterici (Wied. Ann. lxix. p. 685 (1899) ; 



Drude's Ann. v. p. 51 (1901)) in his first equation : 



This term could be interpreted as indicating that the 

 attraction between molecules varied effectively as the inverse 

 cube of the distance. The above equation yields the relations 

 v c =4b y and RT c /p c r c = 3*75, being thus in much better agree- 

 ment with experiment than van der Waals' equation in 

 respect of these quantities. 



* See a paper by Cotton and Mouton, Journ. de Physique, [5] i. p. 40 

 (1911). 



I 2 



