or some different effect: and in either case it will be impossible to give any sufficient reason why we should confine the population to the surface of a planet. If gravity have not, upon any set of beings, the effect which it has upon us, such beings may live upon the surface of Saturn, though it be mere vapor: but then, on that supposition, they may equally well live in the vast space between Saturn and Jupiter, without needing any planet for their mansion. If we are ready to suppose that there are, in the solar system, conscious beings, not subject to the ordinary laws of life, we may go on to imagine creatures constituted of vaporous elements, floating in the fiery haze of a nebula, or close to the body of a sun; and cloudy forms which soar as vapors in the region of vapor. But such imaginations, besides being rather fitted for the employment of poets than of philosophers, will not, as we have said, find a population for the planets; since such forms may just as easily be conceived swimming round the sun in empty space, or darting from star to star, as confining themselves to the neighborhood of any of the solid globes which revolve about the central sun. 18. We should not, then add anything to the probability of inhabitants on the other planets of our system, even if we were arbitrarily to assume unlimited changes in the laws of nature, when we pass from our region to theirs. But probably, all readers will be of opinion that such assumptions are contrary to the whole scheme and spirit of such speculations as we are here presuming:--that if we speculate on such subjects at all, it must be done by supposing that the same laws of nature operate in the same manner, in planetary, as in terrestrial spaces;--and that as we suppose, and prove, gravity and attraction, inertia and momentum, to follow the same rules, and produce the same effects, on brute matter there, which they do here; so, both these forces, and others, as light and heat, moisture and air, if, in the planets, they go beyond the extremes which limit them here, yet must imply, in any organized beings which exist in the planets, changes, though greater in amount, of the same kind as those which occur in approaching the terrestrial extremes of those elementary agents. And what kind of a population that would lead us to suppose in Jupiter or Saturn, Mars or Venus, the reader has already seen our attempt to determine; and may thence judge whether, when we go so far beyond the terrestrial extremes of heat and cold, light and dimness, vapor and water, air and airlessness, any population at all is probable.