100 Prof. Norton on Molecular Physics. . 



attractions will have a finite value, and be directed inward to- 

 ward the line of the centres. This resultant will increase in 

 value as the distance from the line of the centres increases, 

 to a certain point n, beyond which it will decrease. The sum 

 of all these resultants will act as a compressing force upon the 

 electric sether about m, and determine its density at that point. 

 At other points, as e, r, s } variously situated in the vicinity of 

 the molecules, the joint attraction of the two will generally exceed 

 the attraction of either molecule alone. It follows, therefore, 

 that the two united molecules will be surrounded by an electric 

 atmosphere of their own, spherical or spheroidal in form, and at 

 the same time that the two individual atmospheres will be 

 materially modified. This atmosphere will have an outer enve- 

 lope, as in the case of a simple molecule. 



If we suppose several molecules thus united, the entire group 

 will have its own proper atmosphere. The extent of this atmo- 

 sphere will depend upon the normal attraction at the surface of 

 the group ; and this will also determine the density of the elec- 

 tric aether in the interstices between the molecules*. 



Let us next inquire into the true nature of the electric polari- 

 zation of molecules. 



A molecule becomes polarized whenever, from any cause, a 

 portion of its electric atmosphere is urged around from one side 

 to the opposite side, — where there is an excess the polarity 

 being positive, and where there is a deficiency, negative. But it 

 is especially important to observe that the act of polarization is 

 distinct from the result. The one is dynamical, the other stati- 

 cal. The act of polarization, too, does not consist simply in a 

 flow of a certain amount of electric sether from the one side to 

 the other of the atom ; in addition to this, a certain quantity of 



* In treating briefly of solidification (p. 383 seqq.), our attention was con- 

 fined chiefly to the union of simple molecules in one homogeneous mass ; 

 but there is good reason to believe that in most cases of solidification, with 

 the exception perhaps of that of perfect crystallization, compound mole- 

 cules are first formed, and that these combine in various modes to form the 

 solid. In every such instance the formation of such groups of molecules 

 should be attended with the evolution of heat. This will be the inevitable 

 result of the compression of the electric aether between the combining mo- 

 lecules (fig. 5), whether the individual atmospheres be compressed or not. 



The heat of combustion and of chemical union generally, has in all pro- 

 bability a similar origin — that is, in a compression of the electric aether 

 between the molecules, or in such a compression combined with a contrac- 

 tion of the individual atmospheres. This topic, and the probable cause of 

 the different effects observed in different instances of combination, will be 

 briefly considered under the head of chemical union. 



The varied forms of crystallization assumed by different substances, 

 under similar circumstances, are probably due in a great degree to the di- 

 versity that obtains in the number and grouping of the individual molecules 

 of which the ultimate compound molecules consist. 



