Molecular Diameters. 25 



"where N' is the index of refraction of the medium formed by 

 a collection of the atoms as a gas such that a gramme-atom 

 occupies volume V, and N is the index of the collection of 

 atoms when reduced to the limiting volume B per gramme- 

 atom, and K the dielectric capacity of the atom = N 2 . C 

 and D are parameters characteristic of each family of metals, 

 while p is the density of the atom. This formula is verified 

 by the experimental data for the metals of the Li and Be 

 families. For the non-metals the relation deduced is (8) 



(X' - 1) V = (N - 1)B = EKB 2 3 uW/pW, 



where E is an absolute constant and u is a number having 

 the values 1, 2, 3, 4 for the halogens from F to I and for the 

 elements in otber families corresponding with these halogens. 

 These results are obtained by assuming that the internal 

 electric fields of atoms are the counterpart of their external 

 fields as ascertained in studies on cohesion. Thus the laws 

 of molecular attraction are strongly confirmed by the present 

 inquiry, while a very definite conception is obtained of the 

 mechanism which is at the basis of radiation. This is as 

 simple as a pendulum, or a galvanometer needle, or a piano 

 string, but the complex of constitutive pairs ©f electrons 

 associated with it must be very elaborate. From considera- 

 tion of the cohesion of the parts of the atom certain con- 

 ceptions as to the structure of the atom are indicated. The 

 kinematical interpretation of Balmer's formula is stated more 

 definitely on the supposition that the vibrating special pair 

 of electrons causes certain standing waves in the atom and 

 controls the positions of their nodes. 

 Melbourne, October 190.4. 



II. Molecular Diameters. By William SUTHERLAND *. 



ALREADY improvements in the fundamental data make 

 it necessary to revise the list of molecular diameters 

 given in the Phil. Mag. [6] xvii. 1909, Feb. p. 320. That 

 list was derived from one calculated by Jeans (Phil. Mag. 

 [6] viii. 1904, p. 692) who took for N, the number of mole- 

 cules in a cm. 3 of gas under standard conditions, the value 

 4 x 10 19 , which was the best obtainable at that date. As he 

 had made no allowance for the effects of cohesional force, I 

 applied that refinement to his calculations. But now from the 

 study of the alpha particle Rutherford finds N = 2'77 x 10 19 , 

 in close agreement with 2*80 x 10 19 found by Planck from 



* Communicated by the Author. 



