Some idea of the distance between the atoms of ponderable matter, when in the form of gas, may be gathered from a remark of Dr. Mann’s in his _Guide to a Knowledge of Life_, at page 13, where he says:—
“It can be shown to be highly probable that the ultimate atoms of gases are at least one hundred times their own diameter asunder even when those gases are held in confined vessels.”
The earth and the moon are, therefore, about three times as near together, in proportion to the diameter of the earth, as two atoms of a gas are, if the above remark be true.
In Sir Isaac Newton’s corpuscular theory of light the atoms emitted from the sun were supposed to follow one another at a distance of about a thousand miles apart! Under such circumstances the impact of two atoms of intersecting rays of light would be a comparatively rare event.
M. Leray asserts that the law of gravitation is only an approximation to the truth, and that it is modified by the volumes of bodies. The proof of this he expects will be found some day in the motions of comets, which rapidly change their volume.
Elective affinity he supposes to depend upon the different forms of crystals, two crystals which present plane faces towards each other being more easily pushed together by the atoms of ether than two crystals in which a solid angle or an edge of one is presented to a plane face of the other.
The sun, planets, fixed stars, nebulæ, &c., are, of course, perpetually riddled through and through, in all directions, by currents of ether. That is why the heavenly bodies gravitate towards each other, as explained in a preceding paragraph.
With respect to reflection at the boundary of space, it is an idea which grows upon you the more you think of it. Enormous as creation is it is impossible to conceive of its having _no_ limit. What, then, is beyond that limit?—Nothing. Not even space in which matter can exist; no _place_ even for matter. On reaching the boundary which separates an entity (for space is an entity) from a nonentity matter must be reflected, if elastic; or it must roll for ever against the boundary of space, if inelastic. This conclusion seems to me inevitable; there is no escape from it.
In the new edition of M. Leray’s book he modifies the theory which I have endeavoured briefly to explain in the foregoing paragraphs by supposing that, instead of one ether, there are two in a state of mixture, the second being a grosser fluid, and its atoms larger than those of the other. It is these larger atoms of the grosser fluid which, by their transversal vibrations, produce the phenomena of light, heat, &c. These larger atoms do not suffer the same swift motion of translation through space as the smaller atoms of the subtler fluid. They have no greater motion of translation than ponderable atoms have.