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seen in Aries, it advances to Taurus, then to Gemini, and so on.

James. How many planets are there belonging to the sun?

Tutor. There are seven, besides some smaller bodies of the same kind discovered during the present century, c represents the sun, the

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nearest to which, Mercury, revolves in the orbit a, nearly circular; next

to him is the beautiful planet Venus, who performs her revolution in the orbit b; then comes the Earth in t; next to which is Mars in e; then Jupiter in the orbit f; afterwards Saturn in g; and far beyond him the Herschel planet performs his revolution in the orbit h. Do you recollect the lines in Thomson's Summer?

and thou, O Sun,

Soul of surrounding worlds! in whom best seen
Shines out thy MAKER! may I sing of thee?

'Tis by thy secret, strong, attractive force,
As with a chain indissoluble bound,
Thy system rolls entire: from the far bourne
Of utmost Herschel, wheeling wide his round
Of fourscore years; to Mercury, whose disc
Can scarce be caught by philosophic eye,
Lost in the near effulgence of thy blaze.

Charles. You have substituted the words Herschel, and fourscore, for

Saturn, and thirty. These lines are descriptive of the figure.

James. For what are the smaller circles, which are attached to several of the larger ones, intended?

Tutor. They are intended to represent the orbits of the several satellites or moons belonging to some of the planets.

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James. What do you mean by the word orbit?

Tutor. The path described by a planet in its course round the sun, or by a moon round its primary planet, is called its orbit. Look to the orbit of the earth in t, and you will see, a little circle, which represents the orbit in which our moon performs its monthly journey.

Charles. Has neither Mercury nor Venus any moon?

Tutor. None have ever been discovered belonging either to Mercury, Venus, or Mars. Jupiter, as you observe by the figure, has four moons: Saturn has seven: and the Herschel (which also goes by the name of Uranus) has six: these for want of room are not drawn in the plate.

Charles. The Solar System then consists of the sun as a centre, round which revolve seven planets, and eighteen satellites or moons. Are there no other bodies belonging to it?

Tutor. Yes, as I just observed, four other planetary bodies have been very lately discovered as belonging to the solar system. These are very small, and named from the astronomers who discovered them, who were Messrs. Piazzi, Olbers, and Harding. They are also called the Ceres Ferdinandea, Pallas, Juno, and Vesta

There are comets also which make their appearance occasionally; and it would be wrong positively to affirm that there can be no other planets be longing to the Solar System; since, besides the four bodies just mentioned, it is only within these forty years that the seventh or the Herschel has been known to exist as a planet connected with this system.

Charles. Who first adopted the system of the world which you have been describing?



was conceived and taught by Pythagoras to his disciples, 500 years before the time of Christ. But it seems soon to have been disregarded, or perhaps totally rejected, till about 300 years ago, when it was revived by Copernicus, and is at length generally adopted by men of science:

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