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Influenced by these considerations, I have endeavoured, in the following Introduction, to open up glimpses, as it were, into one or two subjects which are very much akin to the main purpose of the work.

The first of these aperçus refers to the globe which we inhabit, considered in its relations, both to the other members of the system it belongs to, and to the universe at large, of which that system itself is but a portion. In this part of the Introduction nothing more is aimed at than a lucid, intelligible statement of acknowledged facts and elementary truths :—such a statement as, to those to whom the subject is not new, may be no unpleasing reminiscence, while to the uninitiated it can hardly fail, on such a theme, to be both interesting and instructive.

To this elementary exposition I have the pleasure of being able to append a series of Tabular Formulæ, which will furnish information and materials for thinking to the most advanced student of Astronomy. For these the reader is indebted to my esteemed colleague Professor Piazzi Smyth. They have the advantage of containing the latest. intelligence from the remote regions of infinite space, and an account of celestial phenomena, and of the various relations which the heavenly bodies stand in to one another, so full and so minutely particular, that ordinary readers, who are not aware of the resources of science, will be apt to feel their astonishment not unmixed with incredulity. And it cannot but give a

high value to these Tables to know, that they are not copied from former works on the subject, but are mostly the results of original calculations instituted for this work.

My own brief account of the heavens is followed by an exposition of the principles on which I conceive that all geographical knowledge ought to be both acquired and communicated, and in accordance with which the descriptive details in the body of the work have been arranged and classified.

Attached to the Introduction will also be found a contribution from the pen of my valued friend Mr Charles Maclaren. It gives a popular, and every reader will agree with me in thinking, a clear and masterly outline of the truths recently unfolded by the science of Geology respecting the physical structure of the globe, the revolutions it has undergone, and the extinct races of animals that dwelt

upon

it before it was rendered fit for the habitation of man.

These different aspects of creation, whether as it exists above us, or around us, or beneath our feet, cannot be regarded as foreign to the ends proposed in a liberal education. They ought all, on the contrary, to be more or less familiar to every one who has a wish to raise himself above the mere drudgery of mechanical manipulation, or to escape the cramping influences of official routine.

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As Mr Keith JOHNSTON and THE PUBLISHERS have done me the honour to announce this volume as an accompaniment to their CLASSICAL ATLAS, I think it right to state, that I can claim no share of the research and labour required in the preparation of that Work : and I feel myself therefore at liberty to express the high opinion I entertain of the skill, judgment, and taste, displayed in the construction of the Maps, in the artistic beauty of the execution, and in the copiousness and accuracy of the general Index.

J. P.

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INTRODUCTION.

Non aliud quis aut magnificentius quaesierit, aut didicerit utilius, quam de stellarum siderumque naturâ.

SENEC. Natur. Quæst. vii. 1.

THE Earth we inhabit is a body nearly globular, resembling in shape an orange, or a bias-bowl. It is one of a number of bodies, similar to it in form, called Planets, which revolve at various distances round the sun, all moving in the same direction, from West to East, in paths or orbits the planes of which differ but little from the plane of the Earth's orbit.1

But besides this progressive movement in space, which carries them with very different degrees of velocity round the Sun as their common centre, the planets have also a rotatory motion, each on its own axis-like the double motion of the bias-bowl as it rolls along the green.

1 The word plane, and the fact stated above, may be rendered intelligible to the young student, by placing before him a couple of hoops, one somewhat smaller than the other, and connecting them by a pin or strong wire, on which as on a pivot they are easily moveable. Each hoop will represent the orbit of a planet, and the space it encloses the plane of that orbit. Suppose the two hoops to be both adjusted to the horizontal level, it will be necessary, in order to assist the learner in comprehending the planetary movements, to raise or depress one of them, so as to make an angle more or less acute where it crosses the other at the wire.

The Sun which dispenses light and heat to all these bodies is itself a spherical body, and has a motion like them on its axis. That it has, moreover, a progressive movement in infinite space, with all the Planets in its train, towards, or round, some point in the Universe, is now regarded by astronomers as a demonstrated truth.

Of the Planets, which, with the central luminary, constitute what is called the solar or planetary system, five besides the Earth were known to the ancients, and received from them the names which they have ever since retained,-Mercury, Venus, Mars, Jupiter, and Saturn. These being the only planets which are visible to the naked eye, we need not be surprised that no addition was made to their number before the invention of the telescope. By the improvements which Sir William Herschel made on that instrument, he was enabled in 1781 to discover, far beyond the orbit of Saturn, that body which has long been received into the number of the planets under the name of Urănus.

In 1846, another planet was added to the list, under circumstances not a little remarkable. Not only was it ascertained that the body, since called Neptune, existed, and at nearly double the distance of Uranus from the Sun, but its exact place in the

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