versally received, because it rationally accounts for and accords with the phenomena of the heavens.

"At the appointed time, when it pleased the Supreme Dispenser of every good gift to restore light to a bewildered world, and more particularly to manifest his wisdom in the simplicity, as well as in the grandeur of his works, he opened the glorious scene with a revival of sound astronomy;”* and raised up Copernicus to dispel the darkness in which it was then involved.

The Copernican system consists of the sun, seven primary, fourteen secondary planets, and the comets.

The seven planets, Mercury, Venus, the Earth, Mars, Jupiter, Saturn, and the Georgium Sidus, move round the sun, in orbits included one within the other, and in the order here used in mentioning their names, Mercury being that which is nearest the sun.

The seven which revolve round the sun as their centre, are called primary planets.

The fourteen planets, which revolve round the primary ones as a centre, and are at the same time. carried round the sun with them, are called secondary planets, moons, or satellites.

The Georgium Sidus is attended by two moons, Saturn by seven, Jupiter by four, and the Earth by one; all of these, excepting the last, are invisible to

* Pringle's Six Discourses to the Royal Society.

The sun is not absolutely at rest, being subject to a small degree of motion, which is considered in larger works on Astronomy.

the naked eye, on account of the smallness of their size, and the greatness of their distance from us.

Mercury and Venus, being within the Earth's orbit, are called inferior planets; but Mars, Jupiter, Saturn, and the Georgium Sidus, being without it, are called superior planets.

The orbits of all the planets are elliptical; but as the principal phenomena of the Copernican system may be satisfactorily illustrated, by considering them as circular, the latter supposition is usually adopted in giving a general idea of the disposition and motion of the heavenly bodies.

Before we enter into a description of the solar sytem, it may be necessary to define what is meant by the axis of a planet; lest the pupil should conceive them to turn on such material axes, as are used in the machines which are contrived to represent the planetary system.

The axis of a planet is a line conceived to be drawn through its centre, and about which it is conceived to turn in the course of its revolution round the sun; the extremities of this line terminate in opposite points of the surface of the planet, and are called its poles; that which points towards the northern part of the heavens, is called the north pole; that which points towards the southern, the south pole. A ball whirled from the hand into the open air, turns round upon a line within itself, while it is moving forward; such a line as this is meant, when we speak of the axis of a planet.

Fig. 1, plate 1, represents the solar system, wherein O denotes the sun; AB, the circle which the nearest planet, Mercury, describes in moving round it; CD, that in which Venus moves; FG, the orbit of the carth; HK, that of Mars; IN, that of Jupiter; OP, that of Saturn; and QR, that of the Georgium Sidus. Beyond this are the starry heavens.

The sun and the planets are sometimes expressed by marks or characters, instead of writing their names at length. The characters are as follow: the Sun, Venus, the Earth, ♂ Mars, Jupiter, Saturn, H Georgium Sidus.

Mercury,

OF THE SUN.

The sun is the centre of the system, round which the rest of the planets revolve. It is the first and greatest object of astronomical knowledge, and is alone enough to stamp a value on the science to which it belongs. The Sun is the parent of the seasons; day and night, summer and winter, are among its surprizing effects. All the vegetable creation are the offspring of his beams; our own lives are supported by its influence. Nature revives, and puts on a ́new face, when it approaches nearer to us in spring; and sinks into a temporary death at his departure from us in winter.

Hence the Sun was with propriety called by the ancients cor cœli, the heart of heaven; for, as the heart is the heart of the animal system, so is the Sun the centre of our universe. As the heart is the

fountain of the blood, and the centre of heat and motion; so is the Sun the life and heat of the world, and the first mover of the mundane system. When the heart ceases to beat, the circuit of life is at an end; and if the Sun should cease to act, a total stagnation would take place throughout the whole frame of nature.

The Sun is placed near the centre of the orbits of all the planets, and turns round his axis in 25 days. His apparent diameter, at a mean distance from the earth, is about 32 minutes 12 seconds.

Those who are not accustomed to astronomical calculation, will be surprized at the real magnitude of this luminary; which on account of its distance from us, appears to the eye not much larger than the moon, which is only an attendant on our earth. When looking at the Sun, they are viewing a globe, whose diameter is 890,000 English miles; whereas the earth is not more in diameter than 7970 miles: so that the Sun is about 1,392,500 times bigger than the earth. Thus, as it is the fountain of light and heat to all the planets, so it also far surpasses them

in its bulk.

If the Sun were every where equally bright, his rotation on his axis would not be perceptible; but by means of the spots which are visible on his pure and lucid surface, we are enabled to discover this motion.

When a spherical body is near enough to appear of its true figure, this appearance is owing to the shading upon the different parts of its surface; for

as a flat circular piece of board, when it is properly shaded by painting, will look like a spherical body; so a spherical body appears of its true shape, for the same reason that the plane board, in the present instance, appears spherical. But if the sphere be at a great distance, this difference of shading cannot be discerned by the eye, and consequently the sphere will no longer appear of its true shape; the shading is then lost; and it seems like a flat circle.

It is thus with the Sun; it appears to us like a bright flat circle, which flat circle is termed the sun's disc. By the assistance of telescopes, dark spots have been observed on this disc, and found to have a motion from east to west; their velocity is greater when they are at the centre, than when they are near the limb. They are seen first on the eastern extremity, by degrees they come forwards towards the middle, and so pass on till they reach the western edge; they then disappear; and after they have lain hid about the same time that they continued visible, they appear again as at first. By this motion we discover not only the time the sun employs in turning round his axis, but also the inclination of his axis to the plane of the ecliptic.*

* The young observer may view the spots of the sun with a refracting telescope of two or three feet, or a reflecting one of 12 inches, 18 inches, or two feet, taking care to guard the eye with a dark glass, to take off the glaring light; or the image or pic ture of the sun, with his spots, may be thrown into a dark room, through a telescope, and received upon a piece of paper placed nearer or further from the glass at pleasure.