times have given us; the extreme tenuity of much of the luminous matter in the skies; the existence of gyratory motion among the stars, quite different from planetary systems; the absence of any observed motions at all resembling such systems; the appearance of changes in stars, quite inconsistent with such permanent systems; the disclosure of the history of our own planet, as one in which changes have constantly been going on; the certainty that by far the greater part of the duration of its existence, it has been tenanted by creatures entirely different from those which give an interest, and thence, a persuasiveness, to the belief of inhabitants in worlds appended to each star; the impossibility, which appears, on the gravest consideration, of transferring to other worlds such interests as belong to our own race in this world; all these considerations should, it would seem, have prevented that old and arbitrary conjecture from growing up, among a generation professing philosophical caution, and scientific discipline, into a settled belief. 34. Some of the moral and theological views which tend to encourage and uphold this belief, may be taken under our more special consideration hereafter: but here, where we are reasoning principally upon astronomical grounds, we may conclude what we have to remark about the Fixed Stars, as the centres of inhabited systems of worlds, by saying; that it will be time enough to speculate about the inhabitants of the planets which belong to such systems, when we have ascertained that there are such planets, or one such planet. When that is done, we can then apply to them any reasons which may exist, for believing that all, or many planets, are the seats of habitation of living things. What reasons of this kind can be adduced, and what is their force with regard to our own solar system, we must now proceed to discuss.[23] FOOTNOTES: [1] Herschel, 866. [2] Ibid. 866. [3] Herschel, 846. [4] Herschel, 848. [5] That these systems have not condensed to _one_ centre, appears to imply a less complete degree of condensation than exists in those systems which have done so. [6] Herschel, 850. [7] Herschel, 847. [8] The density of the sun is about as great as the density of water. [9] Herschel, 827-832. [10] _Cosmos_, III. 169, 205, and 641. [11] Ibid., III. 172 and 252. [12] _Astron. Soc. Notices_, Dec. 13, 1850. [13] See Grant's _Hist. of Physical Astronomy_, p. 538. [14] I am aware of certain speculations, and especially of some recent ones, tending to show that even our Sun is wasting away by the emission of light and heat; but these opinions, even if established, do not much affect our argument one way or the other. [15] Chalmers' _Astron. Disc._ p. 39. [16] Hersch. 820. [17] The periodical character of this star was discovered by David Fabricius, a parish priest in East Friesland, the father of John Fabricius, who discovered the solar spots. (_Cosmos_, III. 234.)