418 Mr. W. Sutherland on the 
5. Contact Difference of Potential, and Mechanism of the 
Storage of Chemical Potential Energy in the Atther. 
6, The Neutron Structure of the dither used for caleula- 
tion of its Density and Rigidity, with deduction of the Velocity 
of Light. 
1. The Electric Origin of Rigrdity. 
The simplest way of showing the electrostatic origin of 
rigidity is the following. Equation (16) of “A Kinetic 
Theory of Solids”’ gives us that | 
QINbM/JcM=4'6, . . . . . 
where 0b is the coefficient of linear expansion, M the atomic 
mass, that of hydrogen being 1,c¢ the specific heat, p the 
density, and J the mechanical equivalent of heat. By means 
of the experimental data this was shown to be approximately 
true for twelve metals, while Zn and Cd give a value almost 
double the 4°6. In my various papers on molecular force 
the characteristic parameter of molecular attraction for many 
substances is tabulated under the heading MJ, in which M is 
the molecular mass and / is 2/3 of the virial parameter for 
unit mass of the substance. With the inverse fourth power 
for the law of molecular attraction lp gives the potential 
energy of unit mass of the substance at “density p- - But as 
molecular attraction is not directly dependent on molecular 
mass, it is better to treat M?/ as a single parameter inde- 
pendent of M. Now in “Further Studies on Molecular 
Force ” (Phil. Mag. | 5] xxxix.) equation (7) is 
M1="61J(M/p)/b. . 
By the law of Dulong and Petit cM has the mean value 
6°4, thus (2) and (3) give 
M2] 
N=2°3 2 kl 
2° ML)? “) 
Now if m is the actual mass of a molecule it may replace 
M in (4). But in “The Hlectric Origin of Molecular At- 
traction?’ it was shown that ml stands for és?, where e is 
the electron charge and s is the distance Heke the positive 
and negative pleetrane forming the electric doublets which 
cause fblecn tar attraction. These electrons can be denoted 
by $ and b. . 
If the dielectric capacity of the medium is K instead of 
1, m@l=e’s’/K. In molecules containing more than one 
atom $ andb are the, Helmholtz valency charges and the 
ionic charges of electrolytes... But in metals each monatomic 
