and their satellites might possibly be accounted for by the operation of the known laws of Nature.

The explanation of the whole theory may be best understood by dividing it into two parts: the first being that which attempts to account for the formation of planets and satellites, on the assumption of the existence of a central sun, and of certain other specified conditions; the second being that which undertakes to account for the formation of the sun itself, on the assumption of the existence of a diffused nebulous matter in space, or, as it has been aptly called, "a universal Fire-Mist.” 1

When the theory is limited to the explanation of the origin of the planets and their satellites, the original condition of our solar system is assumed to have been widely different from what it now is; the sun is supposed to have existed for a time alone, to have revolved upon his axis, and to have been surrounded with an atmosphere expanded by intense heat, and extending far beyond the limits of our system as it now exists. This solar atmosphere revolved, like the sun itself, around its axis; but its heat, constantly radiated into sidereal space, gradually diminished, and the atmosphere being contracted in proportion as it cooled, the rapidity of its rotation was accelerated, until it reached the point at which the central- attraction was overcome by the centrifugal force, and then a zone of vapor would be detached or thrown off, which might either retain its form as a nebulous ring, like the ring of Saturn, or first breaking into fragments, from some want of continuity in its structure, and afterwards coalescing into one mass, might be condensed into a planet as the vapor continued to cool. These rings or planets, thus detached from the central atmospheric mass, would continue to revolve, in virtue of the force originally impressed upon them, and their motion would be nearly circular, in the same plane and in the same direction with that

1 "Vestiges of the Natural History of Creation,” p. 17.

of the sun. The first planet, so formed, must have been that at the extreme limit of our solar system; the second the next in point of remoteness from the centre, and so on; each resulting from the operation of the same natural laws, and emerging into distinct existence at that precise point in the gradual cooling and contraction of the atmosphere at which the centrifugal became stronger than the centripetal force. But each planet might also be subjected to the same process of cooling and contracting, and might therefore throw off, under the operation of the same mechanical laws, zones of vapor more or less dense, which might consolidate into moons or satellites, and which should also revolve, like the planets, round their primary. Thus, Uranus has six satellites, and Saturn seven; while the latter has also thrown off two zones so perfectly uniform in their internal structure that they remain unbroken, and constitute a double ring around the planet.

In this first form of the theory, which assumes the existence of the sun and its atmosphere, and the rotation of both round an axis, La Place sought to give a scientific form to the speculations of Sir William Herschell on the condensation of Nebulæ, by proving simply the dynamical possibility of the formation of a planetary system by such means, according to the known laws of matter and motion; but he did not affirm the scientific certainty of his conjecture, and far less the actual production of the solar system in this way. He has been followed by M. Comte, who has attempted to furnish, if not a complete demonstration, at least a plausible mathematical verification, of the hypothesis.1 Utterly excluding all supernatural agency in the work of creation, he equally excludes from the problem which

1 AUGUSTE COMTE, "Cours de Philosophie Positive," II. 363, 376. The merits of this attempt are very differently estimated by two competent authorities; by PROFESSOR SEDGWICK in the "Edinburgh Review," No. 82, p. 22; and by SIR DAVID BREWSTER in the "North British Review," No. 3, p. 476.

he attempts to solve, the origin of the sun and its atmosphere; and confining himself to the task of accounting, in the way not of demonstrative certainty, but merely of plausible hypothesis, for the formation of the planets and satellites of our solar system, he conceives the theory of La Place to be susceptible of such a numerical verification as is sufficient to give it a high degree of verisimilitude. Assuming that the periodic time of each planet must be equal to that of the portion of the solar atmosphere of which it was formed at the era when it was thrown off, and combining the theorems of Huygens on the measure of centrifugal forces with Newton's law of gravitation, he establishes a simple equation between the time of the rotation of each zone or section of the solar atmosphere, and the distance of the corresponding planets. On applying this equation to the various bodies of our system, he found that the periodic time of the moon agrees, at least within the tenth of a day, with the duration of the earth's revolution, when her atmosphere is supposed to have extended to the moon; and that the periodic times of the planets maintain a similar correspondence with what must have been the duration of the solar revolution when they were severally thrown off from its atmosphere. It it the less necessary, however, to enter on a detailed exposition of his argument, because he admits that it can afford at the utmost only a probable proof of an hypothesis; and further, because it is expressly limited to the production of the planets and their satellites, while not only is the existence of the solar atmosphere presupposed, but also its existence in a certain state, and with several determinate conditions; while no account whatever is given of the origin either of the sun or its atmosphere, and none of the laws or conditions on which the whole process of development is confessedly dependent.

But the author of "The Vestiges" takes a much wider range, and attempts a more arduous task. He seeks to account for the origin both of suns and of solar systems by the agency

of natural laws. Not content with the more limited form of the theory, which M. Comte holds to be the only legitimate or practical object of scientific treatment, he holds that the origin of the sun itself, and the forms, the positions, the relations, and the motions, of all the heavenly bodies, may be accounted for by supposing a previous state of matter, fluid or gasiform, subject only to the law of gravitation. 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,”1 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. The existence of such a luminous matter being assumed, and it being further supposed that it was not entirely uniform or homogeneous, but that it existed in various states of condensation, and that it had certain nuclei established in it which might become centres of aggregation for the neighboring diffused matter," the author attempts to show that "on such centres a rotatory motion would be established wherever, as was the most likely case, there was any obliquity in the lines of direction in which the opposing currents met each other; that this motion would increase as the agglomeration proceeded; that at certain intervals the centrifugal force, acting on the remoter part of the rotating mass, would overcome the agglomerating force; and that a series of rings would thus be left apart, each possessing the motion. proper to itself at the crisis of separation. These, again, would only continue in their annular form, if they were entirely uniform in their internal structure. There being many chances against this, they would probably break up in the first instance, and be thereafter "agglomerated into one or several masses,

1 "Vestiges," p. 11, 23.

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which would become representatives of the primary mass, and perhaps give rise to a progeny of inferior masses." In support of this theory, reference is made to the existence, at the present moment, of certain cloud-like nebulæ, or masses of diffused luminous matter, exhibiting a variety of appearances, as if they were in various degrees of condensation, and which are described as "solar systems in the process of being formed” out of a previous condition of matter. And the observations of M. Plateau, of Ghent, are adduced as affording an experimental verification of some parts of the theory, and, especially, as serving to explain the spherical form of the planets, the flattening at the poles, and the swelling out at the equator.

It does not belong to our proper province, nor is it necessary for our present purpose, to discuss the merits of this theory, considered as a question of science. This has been already done, with various degrees of ability, but with unwonted unanimity, by some of the ablest men of the age, — by Whewell, Sedgwick and Mason, in England, by Sir David Brewster and Mr. Miller, in Scotland, and by Professor Dod and President Hitchcock, in America. But, viewing it simply in its relation to the Theistic argument, we conceive that the adverse presumption which it may possibly generate in some minds against the evidence of Natural Theology, will be effectually neutralized by establishing the following positions:

1

That it is a mere hypothesis, and one which, from the very nature of the case, is incapable of being proved by such evidence as is necessary to establish a matter of fact.

That the progress of scientific discovery, so far from tending

"

1 WHEWELL, "Indications of a Creator." SEDGWICK'S Discourse," 5th edition. Edinburgh Review," No. 82. SIR D. BREWSTER, “North British Review," No. 3. PROFESSOR Dod, "Princeton Theological Essays," second series. H. MILLER, "Footprints of the Creator." T. MONCK MASON, "Creation by the Immediate Agency of God.”