The Unseen World and Other Essays [8]
whether it is as infinite as space itself, we cannot surmise. If it be limited, the possible dispersion of radiant energy is limited by its extent. Heat and light cannot travel through emptiness. If the ether is bounded by surrounding emptiness, then a ray of heat, on arriving at this limiting emptiness, would be reflected back as surely as a ball is sent back when thrown against a solid wall. If this be the case, it will not affect our conclusions concerning such a tiny region of space as is occupied by the solar system, but it will seriously modify Sir William Thomson's suggestion as to the fate of the universe as a whole. The radiance thrown away by the sun is indeed lost so far as the future of our system is concerned, but not a single unit of it is lost from the universe. Sooner or later, reflected back in all directions, it must do work in one quarter or another, so that ultimate stagnation be comes impossible. It is true that no such return of radiant energy has been detected in our corner of the world; but we have not yet so far disentangled all the force-relations of the universe that we are entitled to regard such a return as impossible. This is one way of escape from the consummation of things depicted by our authors. Another way of escape is equally available, if we suppose that while the ether is without bounds the stellar universe also extends to infinity. For in this case the reproduction of nebulous masses fit for generating new systems of worlds must go on through space that is endless, and consequently the process can never come to an end and can never have had a beginning. We have, therefore, three alternatives: either the visible universe is finite, while the ether is infinite; or both are finite; or both are infinite. Only on the first supposition, I think, do we get a universe which began in time and must end in time. Between such stupendous alternatives we have no grounds for choosing. But it would seem that the third, whether strictly true or not, best represents the state of the case relatively to our feeble capacity of comprehension. Whether absolutely infinite or not, the dimensions of the universe must be taken as practically infinite, so far as human thought is concerned. They immeasurably transcend the capabilities of any gauge we can bring to bear on them. Accordingly all that we are really entitled to hold, as the outcome of sound speculation, is the conception of innumerable systems of worlds concentrating out of nebulous masses, and then rushing together and dissolving into similar masses, as bubbles unite and break up--now here, now there--in their play on the surface of a pool, and to this tremendous series of events we can assign neither a beginning nor an end.
[3] Fortnightly Review, April, 1875.
We must now make some more explicit mention of the ether which carries through space the rays of heat and light. In closest connection with the visible stellar universe, the vicissitudes of which we have briefly traced, the all-pervading ether constitutes a sort of unseen world remarkable enough from any point of view, but to which the theory of our authors ascribes capacities hitherto unsuspected by science. The very existence of an ocean of ether enveloping the molecules of material bodies has been doubted or denied by many eminent physicists, though of course none have called in question the necessity for some interstellar medium for the transmission of thermal and luminous vibrations. This scepticism has been, I think, partially justified by the many difficulties encompassing the conception, into which, however, we need not here enter. That light and heat cannot be conveyed by any of the ordinary sensible forms of matter is unquestionable. None of the forms of sensible matter can be imagined sufficiently elastic to propagate wave-motion at the rate of one hundred and eighty-eight thousand miles per second. Yet a ray of light is a series of waves, and implies some substance in which the waves occur. The substance required is one which seems to possess strangely contradictory properties.
[3] Fortnightly Review, April, 1875.
We must now make some more explicit mention of the ether which carries through space the rays of heat and light. In closest connection with the visible stellar universe, the vicissitudes of which we have briefly traced, the all-pervading ether constitutes a sort of unseen world remarkable enough from any point of view, but to which the theory of our authors ascribes capacities hitherto unsuspected by science. The very existence of an ocean of ether enveloping the molecules of material bodies has been doubted or denied by many eminent physicists, though of course none have called in question the necessity for some interstellar medium for the transmission of thermal and luminous vibrations. This scepticism has been, I think, partially justified by the many difficulties encompassing the conception, into which, however, we need not here enter. That light and heat cannot be conveyed by any of the ordinary sensible forms of matter is unquestionable. None of the forms of sensible matter can be imagined sufficiently elastic to propagate wave-motion at the rate of one hundred and eighty-eight thousand miles per second. Yet a ray of light is a series of waves, and implies some substance in which the waves occur. The substance required is one which seems to possess strangely contradictory properties.