circle h. Do you recollect the lines in Thomson's Summer?

-and thou, O Sun;

Souk 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 disk
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.

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 (Fig. 2.) 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 the Georgium Sidus) has six; these for want of room are not drawn in the plate.

Charles. The Solar System then consists of the sun as the centre, round which revolves 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 gentlemen 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 belonging to the solar system; since, besides the four bodies just mentioned, it is only within these thirty 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?

Tutor. It 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:

The sun revolving on his axis turns,
And with creative fire intensely burns;
Impell'd the forcive air, our earth supreme'
Rolls with the planets round the solar gleam ;]
First Mercury completes her transient year,
Glowing refulgent, with reflected glare;
Bright Venus occupies a wider way;
The early harbinger of night and day:
More distant still our globe terraqueous turns,
Nor chills intense, nor fiercely heated burns.
Around her rolls the lunar orb of light,
Trailing her silver glories through the night:
Beyond our globe the sanguine Mars displays
A strong reflection of primeval rays;
Next belted Jupiter far distant gleams,
Scarcely enlighten'd with the solar beams:
With four unfix'd receptacles of light

He towers majestic through the spacious height;
But farther yet the tardy Saturn lags,
And seven attendant luminaries drags;
Investing with a double ring his pace,
He circles through immensity of space.

CHATTERTON.

CONVERSATION XXVII.

Of the Figure of the Earth.

Tutor. Having, in our last conversation, given you a description of the Solar System in general, we will now proceed to consider each of its parts separately; and since we are most of all concerned with the earth, we will begin with that body.

James. You promised to give us some reasons why this earth must be in the form of a globe and not a mere extended plane, as it appears to common observation.

Tutor. Suppose you were standing by the sea-shore, on a level with the water, and at a very considerable distance, as far as the eye can reach, you observe a ship approaching, what ought to be the appearance, supposing the surface of the sea to be a flat plane?

Charles. We should, I think, see the whole ship at once, that is, the hull would be visible as soon as the top-mast.

Tutor. It certainly must, or indeed rather sooner, because the body of the vessel being so much larger than a slender mast, it must necessarily be visible at a greater distance.

James. Yes, I can see the steeple of a church at a much greater distance than I can discern the iron conductor which is upon it, and that I can perfectly see long before the little piece of gold wire, which is fixed at its extremity, is visible.

Tutor. Well, but the top-mast of a vessel at sea is always in view some little time before the hull of the vessel can be discerned. Now, if the surface of the sea be globular, this ought to be the appearance, because the protuberance or swelling of the water between the vessel and the eye of the spectator, will hide the body of the ship some time after the pendant is seen above.

Charles. In the same way as if a high building, a church for instance, were situated on one side of a hill, and I was walking up on the opposite side, the steeple would come first in sight, and, as I advanced towards the summit, the other parts would come successively in view.

Tutor. Your illustration is quite to the purpose: in the same way two persons, walking up a hill on the opposite sides, will perceive each other's heads first; and as they advance to the top, the other parts of their bodies will become visible. With respect to the ship, the following figure will convey the idea very completely. (Plate v. Fig. 3.) Suppose c A в represent a small part of the curved surface of the sea: if a spectator stand at B, while a ship is at c,