Prof. Norton on Molecular Physics. 99 



as the diameter of this envelope; and we shall use these terms in 

 the samesense hereafter, unless the exception is distinctly specified. 



The outer electric envelopes of molecules serve to establish 

 an electric communication between them, and play an important 

 part in all electric phenomena. By their pressure upon the inner 

 envelopes, or the atmospheres so called, of the molecules, they 

 develope a force of electric repulsion exerted outward at the sur- 

 face of each atmosphere. This is the force already recognized 

 as one of the molecular forces (p. 196). It has its immediate 

 origin in the compression of the atmosphere at or near its sur- 

 face, by the outer envelope, which increases the repulsive action 

 of the upper portion of the atmosphere, and so brings into ope- 

 ration an effective repulsion at this surface, where otherwise the 

 effective force would be zero. It is to be borne in mind that 

 the attraction of the central atom is dynamical in its effects, and 

 that attendant upon its exertion the outer envelopes will have 

 an inward and outward movement ; but such alternate move- 

 ments will, when propagated outward, neutralize each other's 

 effects, unless a secondary force is developed in the process. 

 Now it is precisely such a force that is developed in the manner 

 just explained ; and this must be propagated by the electric aether 

 of the outer envelope, or the interstitial electric sether of bodies, 

 as a wave-force*. 



We have seen that the attraction exerted by the atom upon 

 its atmosphere proper, by forcing outward a portion of the uni- 

 versal aether near the surface of the atom, developes at the same 

 time an effective molecular attractive force, and what we have 

 called the force of heat-repulsion. From the difference that ob- 

 tains in the circumstances under which these forces and the 

 above-mentioned force of electric repulsion originate, it is highly 

 probable that their constants (n and m, p. 200) would be different. 



To pass now to the case of a compound molecule : let a and b 

 (fig. 5) be two similar molecules, held in equili- Fig. 5. 



brium by their mutual actions, and let us inquire 

 into the condition of the electric aether on the 

 line crossing perpendicularly the line of their 

 centres, at its middle point m. At m the attrac- 

 tions of the two molecules for an atom of electric 

 aether there will neutralize each other ; but at all 

 other points of this line the resultant of the 



* The pulses of heat that are received from extraneous sources, and pass 

 from molecule to molecule, augment this force of atmospheric repulsion. 

 Accordingly the value of the " constant " m of this force (p. 199) depends 

 not only upon the attractive force, size, and perhaps other peculiarities of 

 the central atom, but also upon the amount of heat received from all ex- 

 traneous sources. External forces of compression or extension, applied to 

 a body, also tend to augment or diminish the value of m. 



H2 



