Sir David Brewster, in his book "More Worlds Than One," says that the doctrine of the plurality of worlds was maintained by almost all the distinguished astronomers and writers who have flourished since the true figure of the Earth was determined: "Giordano Bruno of Nola, Kepler, and Tycho believed in it; and Cardinal Cusa and Bruno, before the discovery of binary systems among the stars, believed also that the stars were inhabited. Sir Isaac Newton likewise adopted it, and Dr. Bentley, Master of Trinity College, in his eighth sermon on the Confutation of Atheism from the origin and frame of the world, has ably maintained the same doctrine. In our own day we may number among its supporters the distinguished names of Laplace, Sir William and Sir John Herschel, Dr. Chalmers, Isaac Taylor, and M. Arago."
The attitude of the intelligent world to-day is well shown in a recent number of London "Nature," where in a review of a book by Wallace, endeavoring to show that this world alone sustains life, the reviewer ends by saying: "To consider this Earth as the only inhabited body in the stellar universe, a reversion to prehistoric ideas, may or may not be an advance, but it will require very strong arguments before we can be brought to consider that its isolation in the Cosmos is indeed a fact." Until the discovery by Schiaparelli of the network of lines in Mars, laid out with seemingly intelligent precision, the arguments for the inhabitability of other worlds were based entirely upon analogy. Sir Richard Owen, the great comparative anatomist, in supporting the contention that life existed in other planets, said: "The grounds of belief vary with the probability of a proposition; if nothing better than analogy can be had—on analogy will belief be based."
Professor O. M. Mitchell, the first director of the Cincinnati Observatory, in his work on "Popular Astronomy," says, in regard to the doctrine of the plurality of worlds: "It would be most incredible to assert, as some have done, that our planet, so small and insignificant in its proportions when compared with other planets with which it is allied, is the only world in the whole universe filled with sentient, rational and intelligent beings capable of comprehending the grand mysteries of the physical universe."
The eminent French astronomer, M. Flammarion, has, in an eloquent passage in his "Plurality of Worlds," portrayed the vastness of the universe and the utter insignificance of our Earth in the immensity of space: "If advancing with the velocity of light[1] we could traverse from century to century this unlimited number of suns and spheres without ever meeting any limit to this prodigious immensity where God brings forth worlds and beings; looking behind, but no longer knowing in what part of the infinite to find this grain of dust called the Earth, we should stop fascinated and confounded by such a spectacle, and uniting our voice to the concert of universal nature we should say from the depths of our soul, Almighty God! how senseless we were to believe that there was nothing beyond the Earth, and that our abode alone possessed the privilege of reflecting thy greatness and honor."
Compare these elevating thoughts with the shrunken attitude of one who has the conceit to imagine that he and his kind are not only alone in the universe but superadds to this monstrous conception the idea that the millions of great suns are designedly waltzing around solely for his edification and amusement, unmindful of the heedless way in which the millions of his race regard the overpowering majesty of the heavens. To the thousand millions that live to-day, and the thousand, thousand millions that have perished in the past, the starry heavens have never excited an emotion grateful, reverent, or curious, unless a flaming comet, or an eclipse of the Sun or Moon occurred, and then with superstitious fear have they gone grovelling in the dust.
An astronomer imbued with Hebraic conceptions of the universe is poorly equipped to appreciate the arguments in favor of life in other worlds. He may be keen in perceiving lines in the spectrum, and the significance of their lateral displacement, but possessed with a belief—the result of early training—that a little two-legged human molecule could command the Sun and Moon to stand still, a realization of his own insignificance, or the possibility of intelligence in other worlds, must forever remain beyond his grasp. Emerson said "the dogmas shrivel as dry leaves at the door of the observatory." They never shrivel for such minds, but grow and flourish with a density that obscures by, its rankness every rational conception of the heavens above. As an illustration of the attitude of such mentalities we have to go back fifty years, for few survive to-day. Edward Hitchcock, Professor of Geology and Theology at Amherst, wrote a book just fifty years ago entitled "Plurality of Worlds," in which he denounces the idea; but observe the precise way in which he lays down the law: "The planets had no vital tendencies, they could have had such given only by an additional act or series of acts of creative power. As mere inert globes, they had no settled destiny to be the seats of life; they could have had such a destiny only by the appointment of Him who creates living things and puts them in the places which he chooses for them" (page 352).
It may be objected that it is useless to bring up these old theological conceptions, as the world has happily gone beyond them, and only in an atavistic manner do we find a few still holding them; nevertheless it may be safely asserted that fifty years hence we shall look back upon the attitude of certain astronomers to-day with much the same pity and amusement which excites us when we regard the attitude of a similar class in the middle of the last century.
Tyndall expresses the universal belief of thinkers in whatever line of work, that life is by no means confined to this Earth. He says: "Whether the other fixed stars have similar planetary companions or not is to us a matter of pure conjecture, which may or may not enter into our conception of the universe. But probably every thoughtful man believes, with regard to these distant Suns, that there is, in space, something besides our system on which they shine."
One class of objectors to the idea that other worlds are inhabited endeavors to show that our position in the universe is unique, that the solar system itself is quite unlike anything existing elsewhere, and, to cap the climax, that our own little world has just the right amount of water, air, and gravitational force to enable it to be the abode of intelligent life, and nowhere else in the broad expanse of heaven can such physical habitudes be found as will enable life to originate or to exist!
In a memoir on the "Evolution of the Solar System," by Professor T. J. J. See, the author, while not denying the possibility of other systems like our own, still considers our system unique. Here are his words: "Therefore, while observation gives us no grounds for denying the existence of other systems like our own, it does not enable us to affirm, or even to render probable, that such systems do exist." Because a number of binary stars have been discovered in which the two stars are nearly equal in mass, and their orbits highly eccentric, he therefore concludes that the millions of stars that stud the heavens are probably without satellites. The unreasonableness of this attitude is emphasized by realizing that these innumerable suns are similar to our own Sun, as revealed by the spectroscope, and have a similar eruptive energy. Professor Newcomb, however, says: "Evidence is continually increasing that dark and opaque worlds like ours exist and revolve around their primaries." Had Mr. See discovered that every star of the many million was accompanied by another star nearly equal in mass, with its marked eccentric behavior, then only would he be justified in his inference that our solar system was indeed unique. When one realizes that the stars are at such unimaginable distances that the highest powers of the telescope reveal even the nearest of them only as points of light—not as disks—and when one further realizes that the satellites of our Sun, even the largest of them, are diminutive globes compared to the vastness of the Sun, it seems unreasonable if not impossible to entertain the idea that none of these remote stars are accompanied by satellites, and that, therefore, this little Sun of ours stands without parallel in the universe.