76 W. A. Norton on Molecular Physics. 
atoms. So far as any polarization of molecules comes into ope- 
ration, we shall hav asion to rk in discussing briefly 
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value of « that obtains when a vapor formed at any 
temperature has its maximum tension, is the distance Od, fig. 1, 
answering to the maximum molecular repulsion, dn; and this 
varies for different temperatures beeause the ratio, oa decreases 
as the temperature rises, (See different yalues of maximum re- 
nulsion answering to different values of the ratio -, given in 
[able 1.) “a 
The process of transition from the solid to the liquid state oc- 
curs at the surface of the mass. As the heat is absorbed, the 
molecules near the surface recede from each other; and when 
this expansion has reached a certain point, the attractive forces 
of the particles at the different orders of distance come success- 
ively into action, being less intercepted by intervening particles. 
At the same time, the individual molecular atmospheres expand, 
or recede from their central atoms, under the action of the heat 
pulses that penetrate to these atoms; and so th 
attractive force of each of these molecules declines, 
- to an effective repulsion from the united action of those below 
it, which is in equilibrium with the tension of the vapor resting 
on the surface; and that this effective rep 
points above the surface, = 
effective repulsion extends to all 
