Electric Origin of Molecular Attraction, 641 



it is impossible to get the electrons to change places without 

 the atoms doing so also. When NaCl is giving the spectrum 

 of Na perhaps both # and b are in Na. In a compound 

 molecule, then, an electric doublet has less freedom of motion 

 than in the molecule of an element gas. On this account 

 the collision of molecules of an element gas is a simpler 

 event than that of compounds. Moreover, in all compounds 

 but the simple binary ones there are several doublets in each 

 molecule, and during a collision a variety of possible com- 

 binations of positions of the doublets will succeed one 

 another, causing an alternation of attractions and repulsions, 

 which leave a different average preponderance of attraction 

 at close quarters than at a distance. Thus below volume k 

 the preponderance of attraction is expressed by a virial 

 — l/2v, and above k by a virial — l/(v-tk), which, when v is 

 large, can be identified with the standard form — l/v. Now 

 this contrast between the behaviour of compound and element 

 gas-molecules at close quarters was verified in the Viscosity 

 of Gases &c. (xxxvi.), where it was found that at close 

 quarters the mutual potential energy of two compound mole- 

 cules is only half of what it would be if they behaved as the 

 molecules of element gases. 



In this way I have sought to explain the most important 

 difficulty in the way of the electric theory of molecular 

 attraction, namely that the attractional virial for compounds 

 appears in the form — l/(v + k) instead of —l/v, which is 

 required by the general theory. Previously (xxxv.) I sug- 

 gested that this phenomenon in compounds might be due to 

 the pairing of compound molecules. This explanation must 

 be withdrawn to be replaced by that of molecular entangle- 

 ment here suggested, an entanglement being only a temporary 

 sort of pairing. 



We proceed now with the investigation of the laws of s. 

 In the case of the haloid compounds of the alkali metals 

 it was shown in " Further Studies" (xxxix.) that to (M 2 /)*, 

 which is proportional to s, the metallic and halogen atoms 

 contribute parts as follow : 



Li. 



Na. 



X. 



Eb. 



Cs. 



F. 



Cl. 



Br. 



I. 



2*4 



3-5 



4-6 



6-0 



7-3 



0-9 



2-1 



2-7 



3-6 



For the Li family these can be written 1*2 (2, 3, 4, 5, 6), 

 and for the F family 09 (1, 2, 3, 4). With the haloid com- 

 pounds of the dyad metals of the Be family, we must 

 remember that (M 2 //2)^ now consists of a part F s due to the 

 halogen atom as given above, and a part F r /2 due to the 

 Phil. Mag. S. 6. Vol. 4. No. 24. Dec. 1902. 2 U 



