THE ELECTRIC AND LUMINIFEROUS MEDIUM. 217 
nuclei which in pondei’able media disturb these lines. This propagation in time 
requires inertia and elasticity for its mathematical expression, and the problem 
of the free mther is to find what kind of each is requisite. 
9. A theory which, like the present one, explains atoms of matter as made up of 
singularities of strain and motion in the aether, is bound to look for an explanation 
of gravitation by means of the properties of that medium ; it cannot avail itself of 
CoTEs’s dogma that gravitation at a distance is itself as fundamental and intelligible 
as any explanation thereof could be. In further development of the illustrative 
possibilities of the pulsatory theory of gravitation, mentioned in the previous 
papers, we can (ideally) imagine the pulsation to have been applied initially over the 
outside boundary of the mthereal universe, and thence instantaneously communicated 
throughout the incompressible medium to the only places that can respond to it, the 
vacuous nuclei of the electrons ; and we can even imagine the pulsations thus 
established as spontaneously keeping time and phase ever after, when the exciting 
cause which established this harmony has been discontinued. 
It has been noticed in Part I, § 103, that gravitation cannot be transmitted by any 
action of the nature of statical stress; for then the approach of two otoms would 
increase the strain, and therefore also the stress, and therefore also in a higher ratio 
the energy of strain which depends on their product, and hence the mutual forces 
of the atoms would resist approach. As gravitation must belong to the ultimate 
constituents of matter, that is on this theory to the electrons, and must be isotropic 
all round each of them, it would appear that no mediate mthereal representation of it 
IS possible except the one here considered. The radially vibrating field might be 
described formally as the magnetic field of the electron considered as a unipolar 
magnet, necessarily of very rapidly alternating type because otherwise a field of 
gravitation would be an ordinary magnetic field. The bare groundwork of this 
hypothesis may thus be formally expressed in Maxwell’s language and developed 
along his lines, by postulating that the electron is not only a centre of steady 
intrinsic electric force, but also a centre of alternating intrinsic magnetic force, 
instantaneously transmitted because it would otherwise involve condensation, each 
force being necessarily radial.* The unsatisfactory feature is that this radial quasi- 
magnetic field is introduced for the sake of gravitation alone, which does not present 
itself as in any direct correlation with other physical agencies. 
The following sections are occupied chiefly with an attempt to logically systematize, 
and in various respects extend, the electric aspect of molecular theory. The preceding 
paper^ dealt mainly with the molecular side of directly aethereal phenomena, such as 
electric and radiative fields; of the present one the earlier part follows up the same 
subject, and the remainder relates to the actions of the molecules of polarized 
* Two steady magnetic poles of like sign would repel each other : but in the case of two poles 
pu sating m the same phases there is also an inertia term in the fluid ethereal pressure, and the 
result IS as stated above. CJ. Hicks, ‘ Proc. Camb. Phil. Soc.,’ 1880, p. 35. 
VOL. CXC.—A. 2 F 
