turn round a single point in the south, as the northern hemisphere appears to turn round the polar

star.

The general appearance, therefore, of the starry heaven is that of a vast concave sphere turning round two fixed points (diametrically opposite to each other, the one in the north, the other in the south) once in twenty-four hours.

Hence it is that the stars, though they keep the same relative places with respect to each other, yet change their situation very sensibly with respect to the horizon; some rising above, others descending below it; some that were invisible, now becoming visible; while, on the other hand, many are disappearing. Some never descend below the horizon; although, as they turn round, they are sometimes nearer to, at others, further from it, describing whole circles about a point above it. If the observer turns himself round, he will find some stars rise only as it were to set again; many describing small arcs, and others larger ones.

THE APPEARANCES OF THE PLANETS.

Besides the fixed stars, there are other bodies in the heavens, which are continually changing their places, both with respect to the stars, and one another; these are called planets. They move among the signs of the zodiac, never departing far from the ecliptic. Their apparent motion is very irregular, confused, and perplexed; sometimes they appear as

going forwards, sometimes backwards, and at others are stationary.

Mercury emits a bright white light, but keeps so near the sun, and is so small, that he is very seldom visible; and when he does make his appearance, his motion towards the sun is so swift, that he can only be discerned for a short time. He appears a little after sun-set, and again a little before sun-rise.

Venus is the most beautiful star in the heavens, known by the names of the morning and evening star. She also, like Mercury, keeps near the sun, though she recedes from him much further, and, like him, is never seen in the eastern quarter of the heavens when the sun is in the western; but always either attends him in the evening, or gives notice of his approach in the morning.

Mars is of a red fiery colour, giving a much duller light than Venus, though he sometimes appears almost equal to her in size. He is not subject to the same limitations in his motions as Venus and Mercury, but appears sometimes very near the sun, at others at a greater distance from him, rising when the sun sets, or setting when he rises.

Jupiter and Saturn likewise often appear at great distances from the sun. The former shines with a bright light, the latter with a pale faint one. The motion of Saturn among the fixed stars is so slow, that unless carefully observed, and that for some time, he will not be thought to move at all.

The Georgium Sidus is the planet discovered by Dr. Herschel. It is reckoned to be twice the dis

tance of Saturn from the sun, but cannot be readily perceived without the assistance of a telescope.

From the preceding observations, any person may easily learn to distinguish all the planets. For if after sun-set he sees a planet nearer the east than the west, he may conclude that it is neither Mercury nor Venus; and may determine whether it be Saturn, Jupiter, or Mars, by the colour and light; by which, also, he may distinguish between Venus and Mercury.

That the light of each planet has its peculiar tinge; and that there are certain fixed stars that have the same teints, was known to the Chaldæans. It is an observation best verified in those countries, where the air is the clearest.

Besides the motions which we observe in all the planets, their apparent magnitudes are very different at different times. Every one must have observed that Venus, though she constantly appears with great splendour, is not always of the same size: but this difference of magnitude is most conspicuous in Mars, it is remarkable in Jupiter, but less so in Saturn and Mercury.

The only phenomena visible to the unassisted sight, besides those already described, are those unexpected obscurations of the sun and moon, called eclipses, of which we shall hereafter speak more particularly.

*

*To these certainly may be added comets, of which, a very remarkable one exhibited in the Autumn of 1807, his striking figure and majestic course in our northern hemisphere.-EDIT.

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I have now described those appearances, which are the most striking to every person who has paid the least attention to what is passing over his head. The tutor would do well in his place, first, to bring his pupil acquainted with the appearances themselves, and then explain them to him by the globe, or some other instrument. It would not be amiss, if he were now to instruct him by practical observations, and shew him, by a small quadrant, how to measure the elevation of the stars, &c. always remembering that young minds are ever active in search of impressions from external objects; and that these are more permanent than those made by words; in the former, the mind energizes, and is brought into action; in the latter, it is in a great degree passive,

ESSAY I.

PART III.

OF THE COPERNICAN OR SOLAR SYSTEM.

AFTER having stated what would be the appearances of the heavenly bodies, if we were placed at the centre of the system, and then given a general view of their phenomena, as seen from the earth; it will now

be

proper to shew how the irregularities that are discovered in one situation are to be reconciled with the harmony and order that would be visible if they were to be seen from the other; or, in other words, to shew why the motions of the planets appear to us so different from what they really are.

One of the ends for which man was formed, is to correct appearances and errors, by the investigation of truth; whoever considers him attentively, from infancy to manhood, and from manhood to old age, will find him ever busy in endeavouring to find some reality, to supply the place of the false appearances, by which he has hitherto been deceived.

It is the business of the present part of this Essay to correct the errors arising from appearances, and to point out truth by a brief detail of the principal parts of the Copernican system, which is now uni