and Electronic Potential Energy. 255 



affect of tliis in the dynamical calculation of the virial of 

 the collisional forces is to subtract b ironi i;, the molecules 

 being assumed to act during collision like perfectly resilient 

 spheres. So the form v-t-k, in which k is added to v, indi- 

 cates that during the collision of compound molecules, there 

 is some cause which lengthens the mean free path, or in 

 other words, reduces the frequency of collisions. A tempo- 

 rary entanglement during collision is the probable cause of 

 this effect. It must be remembered that though we assign a 

 certain electric moment to the whole molecule, the atoms 

 contribute to this electric moments of their own according 

 to laws investigated in my papers on molecular attraction. 

 The great distinction between the molecules of element gases 

 and those of compound gases is this, that in the diatomic 

 element gases the two atoms are identical. Although con- 

 sisting of two atoms the molecule of an element gas, while 

 not homogeneous, is more nearly homogeneous than that of 

 a compound. When two compound molecules are colliding, 

 the permanent electrical differences amongst the atoms may 

 prevent the electric fields of the whole molecules from ad- 

 justing themselves as they do when the molecules are far 

 apart. It may be more an affair of the atoms in contact 

 than of the whole molecule. Thus the effective moments of 

 the molecules in contact may be different from what they 

 are when the molecules are separate. We can account for 

 the virial of the attractions taking the form 3//2(u + A:) 

 instead of 3l\2v, if we write that form (^M\2v){v\(y+ k)} and 

 interpret the factor vl(v + k) as expressing the change which 

 takes place in the e 2 s 2 of 6pe 2 s 2 jm 2 in (2) with changing 

 distance between neighbour molecules, that is, with changing 

 v. This change in es may sometimes be partly of the nature 

 of an effect of mutual induction, but it seems to me that in 

 the collisional virial the change of form from v — b to v-\-k is 

 suggestive rather of entanglement during molecular encounter, 

 the atomic electric fields being thrown into a confusion which 

 on the averages causes the colliding molecules to have smaller 

 total electric moments effective than when they are free. 

 The equation for ethylene shows the transition from the type 

 for elements to that for compounds. As 0H 4 ranges itself 

 with the element gases, we infer that the electric fields of C 

 and of 4H are united up into one simple field like that of 

 the element gases. In the paper cited it is shown that down 

 to v = k the virial of molecular attractions has the form 

 l\{v + k) when the factor 3/2 is omitted. When v — k it is 

 lj'2k } and for values of v less than k it is l\Zv. Thus in 

 typical compounds I in the virial of the attractions and in the 



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