being the centre of the system: hence it is also called the Solar system; Sol, being the Latin for the Sun.

With this system I shall begin, and shall treat of it in such manner as I conceive will be best adapted to the accomplishment of our present object, namely, that of storing our minds with the great and leading truths of Astronomy. But if we were about to form ourselves for practical Astronomers, for observers of the heavenly bodies, I should certainly have begun with some consideration of those more distant luminous objects which we term Fixed Stars, since they form the points from which, in that case, all our observations would have been dated. Of the Solar system, the fixed stars form no immediate part: we shall accordingly take a separate view of what is known of them. It may however here be permitted to indulge in a few general observations respecting them. Their immense number, their vast distance from the Sun as the centre of a system, the knowledge that their light is not borrowed from the Sun (on all of which points we shall hereafter insist), all conspire to induce the supposition that the fixed stars may be the suns of other systems;-and therefore, that which we call the Solar system, is called so rather because it is our own, than because it is the only one. In this point of view, our solar system is to be considered as a member of the grand universal system.

Of our Solar system, then, the Sun is the centre, and the planets and comets move around it, at different distances.

We shall first proceed to take a general view of this System Of the Sun itself-Of the order in which the Planets move-their distance from the Sun-their respective periods of revolution-their dimensions; and

after taking this general view, we shall again take up the consideration of each, beginning with the Sun, and shall descend into the particulars of what is known respecting them.

In the very brief and general view I am now about to take of this system, we shall have occasion to speak of the dimensions and distances, and velocities of the bodies composing it, with as much confidence and familiarity as though it were possible to determine them with the same ease as the distance of one place from another on the earth. It is almost needless to remark that the knowledge of all these points has been arrived at by a combination of the utmost powers with which the human mind is gifted. If however we were to pause for a moment, to reflect on what hourly and daily passes before our eyes, we should be enabled to form some notion that the heavenly bodies must be very large,— very distant from the earth,-and that the velocities with which they move must be very great.

We will for a moment assume that the earth is, as to us inhabitants it appears to be,—fixed in the midst of an immense sphere of glittering orbs rolling around it. Let us then advert to the fact that the whole circle, including the Sun and the Planets, seems to complete that revolution in 24 hours. Now, if we suppose the Sun and the Stars to be distant from the centre of the earth, only 40 times the earth's diameter (which is about 8000 miles), they must in that case, supposing them to move round the Earth, move in a circle at least one million of miles in circumference; and in order to complete this circle in 24 hours, they must move at the rate of more than 40,000 miles every hour. But this calculation is far within the truth, for the sun is known, from the most

unquestionable evidence, to be at a very much greater distance. But if we suppose him to be only at the distance of one million of miles, the light and heat we derive from him, and his apparent size, sufficiently prove that his bulk must be enormously great.

Thus, the due consideration of what daily passes, or seems to pass before our eyes, will in some measure prepare us to receive the great truths of Astronomy. But even to the most reflecting mind, these truths are of a nature too vast for comprehension. In almost every thing that we justly comprehend, there is some standard of comparison; something to which we can compare the object of our interest. But if a mole-hill be no standard by which to form a just estimate of the size of a mountain; if we cannot measure the relative circumstances of the objects of our sight and of our touch, how is it possible that we should find a standard for those which are objects of the sight alone? What adequate notion have we of millions of miles ;-of a body many millions of miles from us ;-of velocities thousands of times greater than that of a cannon-ball ;-or what notion can we form of open, endless space? Of truths too vast, too sublime for our just comprehension, we must be prepared to hear, for of such truths does Astronomy consist.

The Sun is computed to be 886,149 miles in diameter, and to exceed the earth in bulk, 1,377,633 times.

Mercury, the nearest planet to the sun, is distant from it 36 millions of miles, and moves round it in 87 days 23 hours, at the rate of 109,000 miles an hour. His diameter is about 3100 miles; his bulk is equal to about 1-16th part of the Earth's.

Venus q, the next in order of distance, is computed to be 68 millions of miles from the sun, and moves round it in 224 days 17 hours, at the rate of 89,000 miles an hour. Her diameter is 7498 miles; being somewhat less than the earth.

The Earth is next in order. It is 95 millions of miles from the Sun, and moves round it in 365 days and 6 hours, at the rate of about 68,000 miles an hour. The diameter of the earth is 7964 miles.

The next is Mars 3, which is computed to be 144 millions of miles from the sun, and goes round it in 1 year, 321 days and 23 hours, at the rate of 55,000 miles every hour. His diameter is 4,218 miles. His bulk is about 1-7th part of that of the earth.

Next succeed four newly discovered planets, Vesta, Juno, Ceres, and Pallas, the largest of which does not exceed 2100 miles in diameter, according to the highest computation. Vesta, the nearest of the four to the sun, is distant from it about 225 millions of miles; Juno, about 253 millions; Ceres ? 263 millions, and Pallas also about 263 millions of miles.

Vesta moves round the sun in about 3 years and 3 quarters. Juno in about 4 years and a quarter. Ceres and Pallas, each in about 4 years 7 months.

Next in distance from the Sun, is Jupiter 4. He is about 495 millions of miles from the Sun, and moves round it in 11 years and 315 days, at the rate of 29,000 miles an hour. His diameter is 89,000 miles, being 11 times that of the earth. The bulk of Jupiter is 1400 times greater than that of the Earth.

Saturn his next. He is about 900 millions of miles from the Sun, and moves round it in about 29 years and a half of our time, at the rate of 22,000 miles

an hour. His diameter is about 79,000 miles-being 9 times greater than that of the Earth. The bulk of Saturn is about 960 times greater than that of the Earth.

The Georgium Sidus H is twice the distance from the Sun that Saturn is, being 1800 millions of miles from him. It moves round the Sun in about 83 years and a half of our time, at the rate of about 15,000 miles an hour. Its diameter is about 34,000 miles, being nearly 4 times that of the Earth. The bulk of the Georgium Sidus is about 80 times that of the Earth.

Thus, there are eleven enormous bodies, termed planets, perpetually dashing through space around the Sun. The term planet is derived from the Greek #λavaw (planao) to wander, the planets being by early observers distinguished as Wandering Stars, in opposition to those which they termed Fixed Stars. The planets are opake bodies, nearly spherical, and, at least in this respect, much resemble the Earth. They have no light of their own, but derive from the Sun, a light, which they reflect: if they shone by a light of their own, they would constantly appear to us round like the Sun, which they do not. They all move round the Sun nearly in circles, but not one of them in a direct circle,—and they all move from west to east.

The

These eleven are termed primary planets; several of them have attendants, called secondary planets or moons; —and these are termed the satellites of the planets they so attend, from the Latin, satelles an attendant. Earth is attended by one moon, Jupiter by four moons, Saturn by seven, and also by a double ring, highly luminous and apparently solid; and the Georgium Sidus has six moons.