44? Mr. W. Sutherland on the 
electrons in contact. If the electrons in the ether, instead 
of being in contact, formed doublets at the centre of massless 
spheres made of ether, the density and rigidity of the whole 
wether due to the doublets would be reduced by a factor 
obtained by raising the ratio of @ to the radius of the ether 
sphere to the power 4. We have of late, however, been 
Permioxiaed again with the conception of a very dense and 
propor tionally rigid gether (for example, Reynolds, ‘Scientific 
Papers,’ vol. 111., finds for his granular medium a density 10°). 
At present we are concerned with working out the conse- 
quences of the electron theory. On being applied to the 
zther it leads to the above density and rigidity, which cannot 
be dismissed for their absurdity merely because of their 
magnitude. Other lines of inquiry will have to furnish the 
data necessary for decisive determinations. 
Although the zether has been likened above to a metal at 
absolute zero, it is different inasmuch as it probably always 
contains as much electrokinetic energy as electrostatic. If 
the two electrons are rotating round their centre of inertia 
with linear velocities u, their total electrostatic energy can be 
immediately written down and their total electrokinetic energy 
obtained according to Heaviside (Phil. Mag. [5] xxvii). 
First, for the electrokinetic energ ey of each electron due to its 
own translatory motion we have eu?/3V7a. Again, if each 
electron has an angular velocity of rotation w abe an axis, 
‘its kinetic energy will be a2o?I/3. 
The potential energy of the electricity of an electron is 
e?/2a. Thus, then, the self-energy of the two electrons is 
2eu2/3V2a + Yo2wT3+eEA/a. . . . (33) 
For their mutual kinetic energy we have ¢?u?/V?r ; if 7 is 
the distance between their centres, and their mutual potential 
energy is —é/r, so that the total mutual energy is 
uP! VA — elt. 3 3) es 
According to the investigations of Thomson, Heaviside, 
Searle, and Abraham the formule for the electrokinetic 
energv hold only when w/V is small. For larger values of 
u/V the kinetic energy is no longer given by half the product 
of an inertia and the square of the velocity. It seems to me, 
however, that there is a promising line of research in 
assuming that for all values of u/V kinetic energy is given 
by the expressions used above, and in deducing what modi- 
fications are required in the fundamental laws of electro- 
magnetism to bring them into harmony with the principle 
that electric kinetic energy is always the prceduct of the 
