Lastly, I submit that the whole of the evidence I have here brought together leads to the conclusion that our earth is almost certainly the only inhabited planet in our solar system; and, further, that there is no inconceivability--no improbability even--in the conception that, in order to produce a world that should be precisely adapted in every detail for the orderly development of organic life culminating in man, such a vast and complex universe as that which we know exists around us, may have been absolutely required. SUMMARY OF ARGUMENT As the last ten chapters of this volume embody a connected argument leading to the conclusion above stated, it may be useful to my readers to summarise rather fully the successive steps of this argument, the facts on which it rests, and the various subsidiary conclusions arrived at. (1) One of the most important results of modern astronomy is to have established the unity of the vast stellar universe which we see around us. This rests upon a great mass of observations, which demonstrate the wonderful complexity in detail of the arrangement and distribution of stars and nebulæ, combined with a no less remarkable general symmetry, indicating throughout a single inter-dependent system, not a number of totally distinct systems so far apart as to have no physical relations with each other, as was once supposed. (2) This view is supported by numerous converging lines of evidence, all tending to show that the stars are not infinite in number, as was once generally believed, and which view is even now advocated by some astronomers. The very remarkable calculations of Lord Kelvin, referred to in the early part of this chapter, give a further support to this view, since they show that if the stars extended much beyond those we see or can obtain direct knowledge of, and with no very great change in their average distance apart, then the force of gravitation towards the centre would have produced on the average more rapid motions than the stars generally possess. (3) An overwhelming consensus of opinion among the best astronomers establishes the fact of our nearly central position in the stellar universe. They all agree that the Milky Way is nearly circular in form. They all agree that our sun is situated almost exactly in its medial plane. They all agree that our sun, although not situated at the exact centre of the galactic circle, is yet not very far from it, because there are no unmistakable signs of our being nearer to it at any one point and farther away from the opposite point. Thus the nearly central position of our sun in the great star-system is almost universally admitted.