sun and the stars. "Igneous vapors, "Igneous vapors," "molten worlds," are reported from the depths of space. "And here," responds the geologist, "in the very world which is our observatory, behold a planetary slag which, some time back, was a 'molten world,' and why not an 'igneous vapor?'" Geology and astronomy join hands and set out in the search for formative worlds which may serve as types of ancient stages of terrestrial history. Later in that history are found the relics of organized creatures, upon which existence has been conferred as the world was fitted for them. The rocky beds of the earth's crust are their tombs, which no sacred scruples restrain the geologist from exploring. With the zoologist upon his right, and the botanist upon his left, he walks among these tombs, and as his companions pronounce the names and alliances of these relics of the organic world he assigns them their respective places in the system of terrestrial preparations, and writes down their respective epochs in the unfolding of the pre-Adamic ages. Thus geology is the resultant of mechanics, thermotics, mathematics, mineralogy, chemistry, astronomy, zoology, and botany, and of all the aids which these sciences summon to their completion and efficiency.

*

It is this conception of the sources of geological information which M. Meunier has brought into requisition in seeking to retrace the evolution of our world to its beginning. He sees in the present condition of the masses of cosmical matter pictures of a former condition of the earth. Drawing upon the body of astronomical facts, which nowhere find a completer popular statement than in the works of Guillemin, Delaunay, or Chambers, he presents us an array of evidences demonstrating a unity, not only of the physical sciences, but of the dominion of the forces of matter, and the intelligence which their activities reveal throughout the utmost breadth of the visible universe. The work of Father Secchi, of the "Roman College," is a charming volume, setting forth in fuller detail every thing which is known respecting the sun as a cosmical body. It embraces the results of the Jesuit father's original observations and speculations upon the sun and its relations to the other heavenly bodies, the earliest records of which may be found scattered through the volumes of the Comtes rendus *Chambers' (Geo. F.) "Descriptive Astronomy." 8vo., pp. 816. Oxford, 1867.

of the Académie des Sciences at Paris from 1863 to 1870. Proctor's work, which appeared almost simultaneously, is written with the same object in view, and, like the other, contains a large infusion of originality. The most marvelous recent advances in cosmical physics have been attained through the use of the spectroscope, which has brought us to a knowledge of the chemical constitution of the stars-a mysterious analysis of matter from which we are separated by millions and billions of miles. The philosophy and forms of the spectroscope, and its applications in spectral analysis, are completely set forth and magnificently illustrated in the work of Schellen, which has the further merit of being the most recent work of its class-a prime quality in reports of scientific progress, characterized by such strides as have been taken by spectroscopic research.*

A survey of the field of scientific truth, as set forth in these works, is well adapted to impress the reader with a conviction that all parts of the visible universe appertain to one system of things; that all have proceeded from one commencement, have been actuated by one impulse, have experienced one history, are bound to a common destination; and that each exemplifies, at every moment of its existence, a stage of evolution which is embraced in the life of every other. These facts, so largely reinforced by recent discoveries, reflect important light upon the question of evolution in the material world; but we propose to confine our attention to the scientific proofs of the co-existent unity of the system of matter.

I. The order and uniformities of the solar system.

(1.) Orbital motions. When we lift our thoughts to the contemplation of the planetary system, of which our earth is a member, we are profoundly impressed by the harmony of those silent but majestic movements executed in the depths of space. The noiseless flight of over a hundred worlds about a common center, passing and repassing without collision or mistake, like partners moving through the orderly mazes of a dance, is a

*This work has been translated into English by the daughters of the astronomer Lassell, and edited, with notes, by William Huggins. An edition of the translation is published by Van Nostrand, New York. The subject is also explained in the works of Proctor and Secchi, cited above. Roscoe's "Spectrum Analysis" is also republished in New York; and information conveniently accessible may be found in Chatfield's "University Series," No. VII, and Lee & Shepard's "HalfHour Recreations in Popular Science," Nos. III, IV, and V.

spectacle well calculated to awaken the emotions of every soul not dead to the sentiment of the sublime.

Eight major planets are known to belong to this system, besides one hundred and twenty-one* minor planets, or asteroids, already discovered. These one hundred and twenty-nine bodies all possess a common orbital motion, from west to east, around the same center, indicating at once that they all belong to one system, regulated by a common law. This conviction is strengthened when we observe that the several orbits possess the same mathematical properties, and that the planets move with corresponding velocities in corresponding parts of their orbits. The orbits, for instance, as expressed by the first law of Kepler, are all ellipses, with the sun situated in one of their foci; while the motions of all the planets are most rapid when in their lower apsides—or those parts of their orbits nearest the sun-and slowest at the opposite extremities of their orbits. Moreover, it appears from mathematical demonstration that the orbital motion of every planet is capable of being caused by the action of two forces-the one a tangential impulse, giving the planet a motion through space, which, from the inertia of matter, would be continuous, the other a constant force, acting in the direction of the center of gravity of the sun, with an intensity varying directly as the masses and inversely as the square of the planet's distance from the sun.

In the next place it will be observed that these orbits all lie in nearly the same absolute plane, suggesting that the planetary movements have all been generated under uniform circumstances. They do not present the spectacle of a swarm of bees, darting in every conceivable direction through space, each actuated by an independent impulse, but rather the consonant and rhythmical movements of a fleet of ships wafted onward by a common breeze.

The orderly arrangements of the planets in respect to distances from the sun must also be noted. They revolve at regularly graduated distances. No clashing can ever occur. Moreover, there are mathematical relations existing between

* The one hundred and eighteenth was discovered, March 15, 1872, by Dr. Luther, of Bilk; the one hundred and nineteenth, April 3, by Prof. Watson, of Ann Arbor; the one hundred and twentieth, April 10, by Borelli, of Naples; and the one hundred and twenty-first, May 12, by Watson.

their velocities, periodic revolutions, and distances from the sun, which are the same for all the planets, and show that the same physical laws extend throughout the solar system. These relations are known as the second and third laws of Kepler, and are thus enunciated:

2. The radius vector of any planet (that is, the line from the planet to the center of its motion) sweeps over equal areas in equal times.

3. The squares of the periodic times of the planets are to each other as the cubes of their mean distances from the sun. These relations are absolutely fixed, and they demonstrate that one dominion extends to the utmost limits of the solar system.

(2.) Satellites. A further correspondence among the several members of this system is the presence of secondary planets revolving about five of them. The earth is accompanied by one satellite, Jupiter by four, Saturn by eight, Uranus by six or eight, and Neptune by one or more. Each satellite revolves about its primary in an elliptic orbit, having the primary planet in one of the foci. The direction of the orbital motion of the satellites, like that of the primaries, is from west to east-except that the satellites of Uranus, and probably of Neptune, exhibit a retrograde motion, from east to west. Could we suppose that the direction of the original motion, in the systems of Uranus and Neptune, was from west to east, and that, by some convulsion, those systems had been bodily overturned, it is apparent that the same actual motion of the satellites, in reference to their primaries, would become a reversed motion in reference to the earth, or any other fixed point in space. This may be illustrated to the eye by the use of a watch. When the watch lies upon its back, the extremities of the pointers represent satellites having a direct motion. In that part of their circuit nearest the observer that motion is from right to left; or, if the person be facing southward toward the belt, where the planetary bodies appear, the motion is from west to east. If now the watch be inverted, so as to lie on its face, the extremities of the pointers move from left to right, a motion which, transferred to the southern heavens, as before, becomes retrograde—that is, a motion from east to west.* If it were * The orbital motions here referred to must not be confounded with the appar

admissible, therefore, to suppose that, since the birth of the systems of Uranus and Neptune, they have undergone an inversion in space, it appears that, notwithstanding the anomaly which they present, their rotations in respect to themselves are in the same direction as the motions of the other systems;* and they are thus original parts of what appears to be a common effect traceable to a general cause responsible for the uniform movements executed throughout the solar system.

(3.) Axial motions. In the next place, all the planetary bodies revolve upon their own axes. It is further remarkable that the axial motions are all in the same direction, and that this direction is the same as that in which the planets revolve in their orbits. It is probable, however, that Uranus and Neptune have a retrograde motion, like their satellites; but this, as before, may be explained on the hypothesis of an inversion of those planets. The sun, also, and moon, have axial rotations in the same direction. We witness, then, the spectacle of probably more than a hundred cosmical bodies, all spinning about their axes with silent and ceaseless velocity, as if some common cause had affected all alike. It is as if the Almighty Hand had taken each in succession and set it whirling, as the boy spins his top upon the floor-each dancing off in due order, but with uniform motion, until the last two are reached, when the planetary tops were inverted, and set to spinning upon their handles. There could scarcely be a spectacle accessible to human intelligence more convincing than the planetary motions, that one plan and one purpose reign throughout the realm of the solar system. Such Kepler confessed to be the impression made upon his mind by the contemplation of the harmonious movements of the heavenly bodies; and such was the confession of Newton. "The wisdom of the Lord is infinite," says Kepler, "as are also his glory and his power. Ye heav

ent daily movement of the heavenly bodies from east to west, caused by the rotation of the earth upon its axis. These orbital motions, as in the case of our own moon, are revealed by the appearance of the same planet, on each successive evening, a little further eastward among the constellations.

*This hypothesis is favored by the circumstance that the inversion of the system of Uranus is not complete-having been carried but little beyond a quarter of a circumference. We might homologize the attitude of these satellites by saying that they have an inclination of about one hundred and one degrees to the plane of their ecliptic, while our moon has an inclination of only five degrees.