CONTENTS. PAGE Constituent Materials of the Earth, and of the other Bodies of Space 18 The Earth Formed-Geological Changes General Considerations respecting the Origin of the Animated Tribes 111 Particular Considerations respecting the Origin of the Animated 3. There was Dry Land long before the occurrence of the first Fossils of 4. There are Species common to different Formations, and an unbroken Succession of Animal Life from the beginning to the present Epoch 5. The Lower Silurian Formation is the Record of an Era of Invertebrate THE BODIES OF SPACE, THEIR ARRANGEMENTS AND FORMATION. It is familar knowledge that the earth which we inhabit is a globe of somewhat less than 8000 miles in diameter, being one of a series which revolve at different distances around the sun, and some of which have satellites in like manner revolving around them. The sun, planets, and satellites, with the less intelligible orbs termed comets, are comprehensively called the solar system; and if we take as the uttermost bounds of this system the orbit of Uranus (though the comets actually have a wider range), we shall find that it occupies a portion of space not less than three thousand six hundred millions of miles in diameter. The mind fails to form an exact notion of a portion of space so immense; but some faint idea of it may be obtained from the fact, that, if the swiftest race-horse ever known had begun to traverse it, at full speed, at the time of the birth of Moses, he would as yet have accomplished only half his journey. It has long been concluded amongst astronomers, that the stars, though they appear to our eyes only as brilliant points, are all to be considered as suns, representing so many solar systems, each bearing a general resemblance to our own. The stars have a brilliancy and apparent magnitude which we may safely presume to be in proportion to their actual size and the distance at which they are placed from us. Attempts have been made to ascertain the distance in some instances by calculations founded B on parallax; that is, the change of relative situation produced on a heavenly object by our planet passing from one part of its orbit to another exactly opposite; it being previously understood that if, upon this base of nearly two hundred millions of miles, an angle of so much as one second, or the 3600th part of a degree, could be raised, the distance might be assumed in that instance as not less than 19,200,000 millions of miles! In the case of the most brilliant star, Sirius, even this minute parallax could not be found; from which, of course, it was to be inferred that that star is farther removed than even this vast distance. In some others, on which the experiment has been tried, it was equally impossible to detect a parallax. We seemed thus to be left in a hopeless state of ignorance regarding the measurements of the sidereal universe, as if it were such a question as man was not destined ever to answer; but at length, in our own time, responses came from several points almost at once. By Professor Henderson, it was ascertained that the star a of the constellation of the Centaur, the third in brightness in our heavens, but in reality a double star, and believed for various reasons to be among those nearest to us, had a parallax of a full second, establishing its distance in miles at about nineteen millions of millions. Afterwards, Bessel assigned a parallax of thirty-one hundredths of a second to the double star 61 Cygni, placing it at a distance nearly 670,000 times that of the earth from the sun.' Such are but the first steps we take in imagination amongst the hosts of orbs by which we are surrounded. If we suppose that similar intervals exist between all the stars, we shall readily see that the space occupied by even the comparatively small number visible to the naked eye must be vast beyond all powers of human conception. The number visible to the eye is about three thousand; but when a telescope of small power is directed to the heavens, a 1 Herschel's Address to Astron. Soc. of London, 1841, and Transactions of that body, vol. xii. great number more come into view, and the number is ever increased in proportion to the increased power of the instrument. In one place, where they are more thickly sown than elsewhere, Sir William Herschel reckoned that fifty thousand passed over a field of view two degrees in breadth in a single hour. It was first surmised by the ancient philosopher, Democritus, that the faintly white zone which spans the sky under the name of the Milky Way, might be only a dense collection of stars too remote to be distinguished. This conjecture has been verified by the instruments of modern astronomers, and some speculations of a most remarkable kind have been formed in connexion with it. By the joint labours of the two Herschels, the sky has been "gauged" in all directions by the telescope, so as to ascertain the conditions of different parts with respect to the frequency of stars. The result has been a conviction that, as the planets are parts of solar systems, so are solar systems parts of what may be called Astral Systems—that is, systems composed of a multitude of stars, bearing a certain relation to each other. The astral system to which we belong, is conceived to be of an oblong, flattish form, with a space wholly or comparatively vacant in the centre, while the extremity in one direction parts into two. The stars are most thickly sown in the outer parts of this vast ring, and these constitute the Milky Way. Our sun is believed to be placed in the southern portion of the ring, near its inner edge, so that we are presented with many more stars, and see the Milky Way much more clearly, in that direction, than towards the north, in which line our eye has to traverse the vacant central space. Nor is this all. A motion of our solar system with respect to the stars, first suggested by Sir William Herschel in 1783, has since been verified by the exact calculations of M. Argelander. The sun is proceeding towards a point in the constellation Hercules. It is, therefore, receding from the inner edge of the ring. Motions of this kind, through such vast regions of space, must be long in producing any change sensible to the inhabitants of our planet, and it is not easy to grasp their |