even, we have to seek aid from our notion of an atom, as something possessing in infinite minuteness, solidity, palpability, weight.  Destroy the idea of the atomic constitution and we should no longer be able to regard the ether as an entity, or at least as matter.  For want of a better word we might term it spirit.  Take, now, a step beyond the luminiferous ether — conceive a matter as much more rare than the ether, as this ether is more rare than the metal, and we arrive at once (in spite of all the school dogmas) at a unique mass — an unparticled matter.  For although we may admit infinite littleness in the atoms themselves, the infinitude of littleness in the spaces between them is an absurdity.  There will be a point — there will be a degree of rarity, at which, if the atoms are sufficiently numerous, the interspaces must vanish, and the mass absolutely coalesce.  But the consideration of the atomic constitution being now taken away, the nature of the mass inevitably glides into what we conceive of spirit.  It is clear, however, that it is as fully matter as before.  The truth is, it is impossible to conceive spirit, since it is impossible to imagine what is not.  When we flatter ourselves that we have formed its conception, we have merely deceived our understanding by the consideration of infinitely rarified matter.

P. There seems to me an insurmountable objection to the idea of absolute coalescence; — and that is the very slight resistance experienced by the heavenly bodies in their revolutions through space - a resistance now ascertained, it is true, to exist in some degree, but which is, nevertheless, so slight as to have been quite overlooked by the sagacity even of Newton.  We know that the resistance of bodies is, chiefly, in proportion to their density.  Absolute coalescence is absolute density.  Where there are no interspaces, there can be no yielding.  An ether, absolutely dense, would put an infinitely more effectual stop to the progress of a star than would an ether of adamant or of iron.

V. Your objection is answered with an ease which is nearly in the ratio of its apparent unanswerability. — As regards the progress of the star, it can make no difference whether the star passes through the ether or the ether through it.  There is no astronomical error more unaccountable than that which reconciles the known retardation of the comets with the idea of their passage through an ether:  for, however rare this ether be supposed, it would put a stop to all sidereal revolution in a very far briefer period than has been admitted by those astronomers who have endeavored to slur over a point which they found it impossible to comprehend.  The retardation actually experienced is, on the other hand, about that which might be expected from the friction of the ether in the instantaneous passage through the orb.  In the one case, the retarding force is momentary and complete within itself — in the other it is endlessly accumulative.