In his chapter on the “Evolution of Celestial Systems” in his book on ‘The Tides,’ Darwin discusses the distribution of the satellites of the Solar System. He says of the evolution of a planet: “We have seen that rings should be shed from the central nucleus when the contraction of the nebula has induced a certain degree of augmentation of rotation. Now, if the rotation were retarded by some external cause, the genesis of a ring might be retarded or entirely prevented.” He then remarks that probably the formation of the Moon was retarded, and in the case of Mercury and Venus, solar tidal friction prevented satellite formation. This explains why Mercury and Venus have no satellites, the Earth only one, Mars two, while the exterior planets have each several satellites.

The theory of tidal friction was extended in 1892 to the explanation of the double stars by the American astronomer, See. See showed by mathematical calculation the effects of tidal friction in shaping the eccentric orbits of the binary stars, the course of evolution being traced from double stars, revolving almost in contact, which the spectroscope reveals, to the telescopic doubles. See’s researches have done much to supplement those of Darwin, who considers that there are two types of cosmical evolution,—the Laplacian, and the “second” or lunar type.

Lowell, in his work on ‘The Solar System’ (1903), adds six congruities to those remarked by Laplace and his successors. These are, “All the satellites turn the same face to their primaries (so far as we can judge); Mercury, and probably Venus, do the same to the Sun; one law governs position and size in the Solar System and in all the satellite systems; orbital inclinations in the satellite systems increase with distance from the primary; the outer planets show a greater tilt of axis to orbit-plane with increased distance from the Sun (so far as detectable); the inner planets show a similar relation.”

The fate of the average solar star is sketched out by Vogel’s classification, and by any evolutionary hypothesis which we may adopt. In the words of Lowell: “Though we cannot as yet review with the mind’s eye our past, we can, to an extent, foresee our future. We can with scientific confidence look forward to a time when each of the bodies composing our Solar System shall turn an unchanging face in perpetuity to the Sun. Each will then have reached the end of its evolution set in the unchanging stare of death. Then the Sun itself will go out, becoming a cold and lifeless mass; and the Solar System will circle unseen, ghostlike, in space, awaiting only the resurrection of another cosmic catastrophe.”

As to what this cosmic catastrophe will be, science gives no definite idea; nor can astronomers say with certainty whether the Universe will come to an end by the extinction of its luminaries, or whether the suns and planets will be brought back to luminosity again; but the human mind shrinks from the idea of a dead Universe. At this point science has said its last word, and must give place to religion. In our day we may repeat with deeper meaning the words of the Scottish astronomer, Thomas Dick: “Here imagination must drop its wing, since it can penetrate no further into the dominions of Him who sits on the Throne of Immensity. Overwhelmed with a view of the magnificence of the Universe, and of the perfections of its Almighty Author, we can only fall prostrate in deep humility and exclaim, ‘Great and marvellous are Thy works, Lord God Almighty.’”

INDEX.

[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] X [Y] [Z]

A Absolute parallax, [158]. Adams, J. C., [78], [116], [117], [118], [119], [120], [140]. Adams, W., [205]. Aerolites, [147], [148], [149]. Airy, Sir G. B., [27], [104], [117], [120]. Aitken, R. G., [202]. Alcyone (η Tauri), [217]. Aldebaran (α Tauri), [151], [166], [170], [172]. Algol (β Persei), [178], [182], [183], [184], [193], [204]. Al-Sufi, [180], [183]. Altair (α Aquilæ), [170]. Anderson, T. D., [191], [192]. Andromeda nebula, [180], [208]. Andromedæ (γ), [201]. Andromedæ (Nova), [180]. Andromedid meteors, [142], [149]. Angström, A. J., [50], [51]. Antares (α Scorpii), [171]. Aquila, [195]. Aquilæ (η), [185], [186]. Arago, F. J. D., [6], [11], [31], [37], [40], [118], [120], [129]. Arcturus (α Bootis), [165], [170]. Arequipa Observatory, [75]. Argelander, F. W. A., [27], [159], [167], [178], [179], [180], [218]. Argo Navis, [221]. Argus (η), [187], [188]. Armagh Observatory, [206]. Asteroids, [19], [62], [97]-102. Astronomer-Royal of Scotland, [134], [155], [191]; of England, [59], [17]; of Ireland, [151], [156]. Astronomy of the invisible, [203]. Aurigæ (Nova), [191], [192], [195]. Auwers, A., [167], [188], [203].

B Babinet, [230]. Baily, F., [159]. Bakhuyzen, H. G., [91]. Ball, Sir R. S., [23], [34], [108], [141], [149], [156], [158], [230]. Barnard, E. E., [19], [95], [107], [108], [110], [111], [113], [136], [191], [211]. Beer, W., [68], [69], [90]. Bellatrix (γ Orionis), [209]. Bélopolsky, A., [87], [110], [166], [185], [186], [204], [205]. Berlin Observatory, [119], [120]. Bessel, F. W., [24], [82], [116], [151], [152], [153], [154], [159], [167], [202], [203]. Betelgeux (α Orionis), [165], [171], [172], [182], [187]. Biela, W., [128]. Biela’s comet, [128], [129], [142], [143], [146], [149]. Birmingham, J., [189]. Bode, J. E., [97], [98], [152]. Bode’s Law, [97]. Boeddicker, O., [77]. Bond, G. P., [103], [109], [130], [136], [207]. Bond, W. C., [109], [112], [120]. ‘Bonn Durchmusterung,’ [159], [160], [218]. Bonn Observatory, [88], [97], [160]. Böotis (ε), [30]. Borisiak, [192]. Boss, L., [168]. Bouvard, A., [115], [116]. Bradley, J., [159], [167]. Brédikhine, T. A., [105], [131], [132], [133], [134], [135]. Brewster, Sir D., [50], [101], [178]. Brinkley, J., [151]. Brünnow, F., [156]. Bruno, G., [35]. Buffon, [103]. Bunsen, R. W., [51]. Burchell, [188]. Burnham, S. W., [201], [202], [212].

C Callandreau, O., [136]. Callandrelli, [151]. Cambridge Observatory, [116]. Campbell, T. (Poet), [2]. Campbell, W. W., [24], [107], [110], [166], [168], [187], [191], [193], [204], [205]. Canals of Mars, [91], [92], [93], [94], [95]. Cancri (ζ), [206]. Cancri (S), [180]. Canis Major, [188]. ‘Cape Durchmusterung,’ [161], [162]. Cape Observatory, [155], [157]. Capella (α Aurigæ), [170], [176], [193], [205]. Carnera, L., [100]. Carpenter, J., [73]. Carrington, R. C., [45], [46], [59]. Cassini, D., [21]. Cassiopeia, [221]. Castor (α Geminorum), [30], [200], [205]. Celoria, G., [202], [218], [221], [223], [224]. Centauri (α), [155], [188], [225]. Centaurus, [221]. Cephei (δ), [178], [182], [185], [186]. Cepheus, [221]. Ceres, [19], [98], [101]. Cerulli, V., [86], [91], [94]. Chacornac, [161]. Challis, J., [116], [119], [120]. Chambers, G. F., [31]. Chandler, S. C., [88], [89], [181], [184]. Chladni, E., [138]. Chromosphere, solar, [55], [56]. Clark, A., [202]. Clerke, Miss A. M., [3], [5], [8], [12], [13], [15], [25], [26], [34], [42], [58], [75], [86], [92], [105], [109], [124], [125], [131], [132], [133], [140], [142], [169], [186], [187], [189]. Clerk-Maxwell, J., [109], [110]. Coggia’s comet, [131], [132], [133]. Comet families, [135]. Comets, [24], [123]-137, [141], [142], [143], [144], [146], [149], [152]. Common, A. A., [107], [209]. Copeland, R., [134], [135], [190], [208]. Cornu, A., [189]. Corona Borealis, [188]. Corona, solar, [55], [57], [64]. Coronæ (Nova), [188], [189]. Crossley, E., [211]. Crux, [221]. Cygni (61), [152], [158]. Cygni (Y), [184], [185]. Cygni (Nova), [189], [190]. Cygnus, [152], [189], [221].