the excessively limited range of the various species of Ammonites throughout the Jurassic and Liassic periods, so that their life's history seems limited to the time necessary for the deposition of a few inches or feet of strata. The succession of the Ammonite forms without any apparent change in the environment, as far as it is possible to carry observation, is one of the most curious problems in the life history of oceanic forms. It is otherwise with land forms and those which inhabited estuaries and shallow waters, there, slight physical changes may easily have brought about the destruction of whole races.

P.S. On reading Dr. Woodward's important remarks, it seems to me that he has rather mistaken the views of the author of this paper. It does not seem to me that Dr. Warring wished to be understood as holding that all life was at any time exterminated over the globe after its original appearance, and was subsequently reintroduced, but that from time to time, certain genera and species were exterminated, or failed to leave descendants.

ORDINARY GENERAL MEETING.*

PROFESSOR LIONEL BEALE, V.P., F.R.S., IN THE CHAIR.

The Minutes of the previous Meeting were read and confirmed.

The following paper was read by the Secretary, in the absence of the Author :

THE NEBULAR AND PLANETESIMAL THEORIES OF THE EARTH'S ORIGIN. By WARREN UPHAM, M.A., F.G.S.Amer. (Hon. Corresponding Member.)

STRONOMY and geology, chemistry and physics, with their very useful arm or ally, spectroscopy, seek together to discover the origin and development of the earth and the moon, of the sun and his retinue of planets, and of the starry universe:

"In the beginning how the heavens and earth

Rose out of chaos."

While we are assured that they "declare the glory of God," and that "all things were made by Him," it has also been learned not less surely that He has worked by His established physical and chemical laws in the creation of suns and worlds. We may partially discern the laws, or methods of working, through which the Creater has made and upholds the myriads of stars and our relatively small, but yet vast, solar system; but beyond all that we know, as, for example, of the laws of gravitation, everywhere lies mystery which baffles our comprehension.

How all matter is influenced by all other matter and drawn toward it, how the earth began and came to its present condition, how the crystal or the plant or the animal grows, "great things and unsearchable, marvellous things without number," proclaim an omnipresent and omnipotent Creator and Ruler.

* Monday, March 20th, 1905.

To learn continually more and more of His thoughts, as revealed in His works, is the highest reward of the student of nature; and increased powers of vision, whether with the telescope or the microscope, open ever-widening fields of knowledge and new problems to be solved. In every direction the search for truth reaches no limit; and in the themes of this paper, although much has been ascertained, infinitely more remains for inquiry.

The nebular hypothesis or theory may well be called the grandest generalization in all the range of the natural sciences. As most elaborately stated by the eminent astronomer and mathematician, Laplace, in his Exposition du Système du Monde, this theory traces the beginning and development of the solar system from an original gaseous nebula, an exceedingly tenuous and intensely heated cloud of matter, extending in a spheroidal form beyond the orbit of Neptune, the outermost planet. By its gravitation and resulting contraction, the nebula is supposed to have acquired a movement of rotation, with polar flattening. Whenever the outer equatorial belt of the revolving nebula attained a centrifugal force exceeding the attraction toward the central mass, a part would be left behind, either as a relatively small revolving nebulous body, or as a ring of such matter, somewhat like the rings of Saturn. Later the ring, if it was at first of that form, would be broken; and, finally, the detached mass would be gathered into a globe, which, in its condensation, would form satellites in the same manner as outer parts of the great central mass formed the successive planets.

Under this theory the principal features of our planetary system, implying unity of origin and development, find a consistent general explanation. Professor Charles A. Young has enumerated these features, which could only have originated by some long process of orderly evolution, as follows:-*

1. The orbits of the planets are all nearly circular.

2. They are all nearly in one plane, excepting considerable
divergence of some of the little asteroids.
3. The revolution of all is in the same direction.

4. There is a curiously regular progression of distances between the planetary orbits.

5. There is a roughly regular progression of density, increasing both ways from Saturn.

*Text-Book of General Astronomy, 1893, p. 515.

6. The plane of the planets' rotation nearly coincides with that of the orbits.

7. The direction of the rotation is the same as that of the orbital revolution, excepting probably the two outermost planets.

8. The plane of orbital revolution of the satellites is nearly coincident with that of the planet's rotation.

9. The direction of the satellites' revolution also coincides with that of the planet's rotation.

10. The largest planets rotate most swiftly.

That these wonderfully harmonious relations of the planets to each other and to the sun, and of the satellites to the planets, could have originated by any fortuitous concourse of matter, like the visits of comets which may come from any part of the heavens, is utterly improbable. There is not one chance in millions for the order of the solar system to have come to pass without a systematic development; but the sublime theory of Laplace, in its main outlines, with modifications as required by further knowledge of astronomical and physical laws, or some other nebular theory, perhaps the one most fully reviewed in this paper, accounts for all this majestic unity of the Creator's plan in launching the earth and its associate planets to revolve around the enormously larger central sun.

Instead of an originally gaseous and very hot condition of the parent nebula, as supposed by Laplace, some prominent English physicists and astronomers have thought that in its earliest definable condition it consisted of meteorites, that is, particles and little masses of solid and cold matter. Sir Norman Lockyer, reasoning from his extensive investigations in spectrum analyses, states this view as follows*:Nebulæ are

really swarms of meteorites or meteoritic dust in the celestial spaces. The meteorites are sparse, and the collisions among them bring about a rise of temperature sufficient to render luminous some of their chief constituents."

Besides the testimony of the spectroscope concerning the characters of the nebulæ, we may consider the rings of Saturn, which are very thin but have great areal extent, as probably a strong evidence of the meteoritic derivation of the p anet and the sun. Richard A. Proctor, after stating the physical

*The Meteoritic Hypothesis, a Statement of the Results of a Spectroscopic Inquiry into the Origin of Cosmical Systems. 1890, p. 322,

impossibilities of the existence and permanence of these unique rings as either solid or liquid continuous bodies, wrote* :

"The sole hypothesis remains that the rings are composed of flights of disconnected satellites, so small and so closely packed that, at the immense distance to which Saturn is removed, they appear to form a continuous mass."

In other words the Saturnian rings are made up of myriads of separately moving small masses, which are doubtless similar to the stony meteorites that fall rarely on the earth.

Again, the origin of the hundreds of asteroids, or minor planets, mostly no more than a few miles in diameter, but including several from 100 to perhaps about 300 miles in diameter, seems very readily explained under this modification of the nebular theory.

Professor Young well says:

"The meteoric theory of a nebula does not in the least invalidate, or even to any great extent modify, the reasoning of Laplace in respect to the development of suns and systems from a gaseous nebula. The old hypothesis has no quarrel with the new."

Another theory, which differs more widely from that of Laplace, has been very recently proposed by Professor T. C. Chamberlin, of the University of Chicago, who names it the Planetesimal Hypothesis. His studies in this direction have been in progress about five years, with publication of preliminary papers, preparing the way for the new hypothesis; but its first somewhat detailed statement in print has appeared since the beginning of the present year. In this latest paper, Professor Chamberlin gives the following principal outlines of his researches for a new and more applicable nebular theory, especially having in view its relation to the origin of the earth.

* Saturn and its System, second edition, revised, 1882, p. 135. + Text-Book of General Astronomy, p. 526.

+ "An Attempt to Test the Nebular Hypothesis by the Relations of Masses and Momenta," in the Journal of Geology, Chicago, vol. viii, pp. 58-73, Jan.-Feb., 1900. "On a possible Function of Disruptive Approach in the Formation of Meteorites, Comets, and Nebulæ, Journal of Geology, vol. ix, pp. 369-392, July-August, 1901.

S"Fundamental Problems of Geology," in Year Book, No. 3, for 1904, of the Carnegie Institution of Washington, published in January, 1905, pp. 195–258.