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The Nebular Cosmogony, which is well characterized by himself as his "version of the romance of Nature," is based on the assumption that "the nebulous matter of space, previously to the formation of stellar and planetary bodies, must have been a universal FIRE-MIST," in other words, a diffused luminous vapor, intensely hot, which might be gradually condensed into a fluid, and then into a solid state, by losing less or more of its heat.
Suppose a world at the distance x, which distance is so great as to make the manifestation of that world weak, milky, nebular.
But under Herschel's treatment the nebular origin of stars first acquired the consistency of a formal theory. He meditated upon it long and earnestly, and in two elaborate treatises, published respectively in 1811 and 1814, he at length set forth the arguments in its favour. These rested entirely upon the "principle of continuity."
The anomalous shortness of the latter may, however, in M. Wolf's opinion, be explained by the "traînées elliptiques" with which Roche supplemented nebular annulation. These are traced back to the descent of separating strata from the shoulders of the great nebulous spheroid towards its equatorial plane.
On some of the nebular lines, which are either straight throughout, or if they change direction do so at an angle, little stars are strung like beads. In one case seven or eight stars are thus aligned, and, as if to emphasize their dependence upon the chain which connects them, when it makes a slight bend the file of stars turns the same way.
He concludes nothing against it, and, what perhaps tells with more weight in the long run, has nothing to substitute for it. In one form or the other, if we speculate at all on the development of the planetary system, our speculations are driven into conformity with the broad lines of the Nebular Hypothesis to the extent, at least, of admitting an original material unity and motive uniformity.
Although this ring theory of the formation of the planets and satellites is not completely proved, the occurrence of such a structure as that which girdles Saturn affords presumptive evidence that it is true. Taken in connection with what we know of the nebulæ, the proof of Laplace's nebular hypothesis may fairly be regarded as complete.
Mr. Gladstone appears to wish that I should enter upon a sort of essay competition with the author of the pentateuchal cosmogony; that I should make a further statement about some elementary facts in the history of Indian and Greek philosophy; and that I should show cause for my hesitation in accepting the assertion that Genesis is supported, at any rate to the extent of the first two verses, by the nebular hypothesis.
Knowing that they are masses of solid or liquid fire, we are tempted to see in them gigantic Catherine-wheels, the fireworks of the gods. What is their relation to the stars? In the first place, their mere existence has provided a solid basis for the nebular hypothesis, and their spiral form irresistibly suggests that they are whirling round on their central axis and concentrating.
Long before the definite estimates were undertaken, geologists had proved that the earth is very, very old, and it can hardly be said that the attempted computations have added much of definiteness to that proposition. They have, indeed, proved that the period of time to be drawn upon is not infinite; but the nebular hypothesis, to say nothing of common-sense, carried us as far as that long ago.
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