original assumption a mere guess, unsupported by all that three centuries of most diligent, and in other respects, successful research, have been able to bring to light. All the knowledge of times succeeding Copernicus, Galileo, and Kepler, (who might well believe the stars to be in every sense suns);—among other things, the disclosure of the history of our own planet, as one in which such grand changes have been constantly going on; the certainty that in by far the greatest 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 of which appears, in the gravest consideration of transferring to other worlds such interests as belong to our race in this world;—all these considerations, it would seem, should have prevented that old and arbitrary conjecture from growing up, among a generation _professing philosophical caution and scientific discipline_, into a settled belief. Finally, it will be time enough to speculate about the inhabitants of the planets which belong to such systems, as soon as we shall have ascertained that there are such planets,—or that there is one such.[105] In the _Dialogue_, written after the first edition of the “Essay” had appeared, the Essayist greatly strengthened the position for which he had contended in it, by an important passage containing the results of the eminent astronomer _M. Struve’s_ recent examination of double stars, and the result of his elaborate and comprehensive comparison of the whole body of facts in stellar astronomy. Among the brighter stars, he arrives at the conclusion, that _every_ FOURTH such star is physically double; and that a completed knowledge of double stars may prove every THIRD bright star to be physically double! And in the case of stars of inferior magnitude, that the number of _insulated_ stars, though indeed greater than that of such compound systems, is nevertheless only three times, perhaps only twice as great. Thus the loose evidence of resemblance between our Sun and the fixed stars becomes feebler the more it is examined; and the assumption of stellar _planetary_ systems appears, when closely scrutinised, to dwindle away to nothing.[106] Now, to so much of the foregoing facts and speculations as are contained in the Essay, from which we have faithfully and carefully extracted the substance, in order that our readers may judge for themselves, Sir David Brewster answers, in effect, and generally in words, thus:—