round before the sun, the length of the day and night taken together is twenty-four hours.

If you pass a piece of straight wire through the middle of an orange, from the stem to the point opposite, and make the orange turn round and round upon the wire, you will have a representation of the AXIS, POLES, and DIURNAL MOTION of the earth. For, as the orange may be made to turn on the wire like a wheel on its axle, so the earth turns round an imaginary straight line passing through its centre, from the north to the south points of its surface. This line is called the AXIS of the earth, and its extreme points or ends, the POLES; the upper, the NORTH pole, because it always points in the direction of the north pole of the heavens; and the lower, the SOUTH pole, for a similar reason.

In turning the orange round the wire, you will observe that every point on its surface moves round and round, except the points in which the wire terminates; and hence these points are called poles, because the earth turns round and round them, while they continue at rest. A top in motion, or a ball made to spin upon a table, may be given as additional illustrations of the earth's motion round its axis and poles. In this case, the uppermost and lowest points of the surface represent the POLES; and an imaginary straight line from one of these points to the other, through the centre, is called the AXIS.

The rotation of the earth on its axis in twenty-four hours from west to east, gives the sun and all the heavenly bodies the appearance of revolving in the contrary direction, that is, from east to west, in the same time; just as you may have observed, while travelling in a carriage or sailing in a boat, that the trees, houses, and other fixed objects, appeared to move past you in the opposite direction, while you fancied yourself to be at rest. If the motion of the carriage or boat in which you are supposed to be placed were perfectly smooth and steady, the more strongly would these appearances pre

Pole.-From a Greek word signifying to turn; whence also pulley, on which the rope turns. Most children confound this term with pole, a long rod or staff. The idea of the axis naturally leads them to make this mistake.

b The north was called upper, because the early astronomers, like ourselves, lived in the northern hemisphere, and consequently, the north pole appeared to them to be the uppermost.

sent themselves, and the less conscious would you be of your own motion. To persons ascending in balloons, it is said that the earth appears to sink beneath the balloon, instead of the balloon appearing to rise above the earth.

In this way, while the earth turns round its axis with a perfectly smooth and uniform motion, the sun, and all the heavenly bodies, appear to us to move in the opposite direction, while the earth appears to be fixed and immovable.

The same phenomena or appearances would be produced if, as was formerly believed, and as the uneducated still think, the sun and all the heavenly bodies revolve round the earth from east to west in twenty-four hours, while the earth itself continues at rest in the centre; but such a supposition is inconsistent with that sublime simplicity which characterizes all the works of the Great Author of Nature. The vicissitudes of DAY and NIGHT, so essential to the enjoyment and relaxation of man, are produced by one of two causes: either the earth turns upon its axis in twenty-four hours, presenting every part of its surface in succession to the sun, or the sun revolves round the earth in the same period of time. No third opinion can be formed on the subject. If the second supposition is correct, then must the sun every twenty-four hours describe a circle of nearly 600 millions of miles in circumference! For the distance of the sun from the earth would be the semi-diameter of the circle which the sun, on the supposition of his revolving round the earth, would have to describe every day-and this distance is known to be nearly 95 millions of miles. But this motion, inconceivable as it is, would be nothing compared to the velocity with which the FIXED STARS would have to revolve; for if the earth does not turn on its axis, then not only the sun, but the ENTIRE UNIVERSE must move round it in twenty-four hours! Now words cannot express, nor imagination conceive the number of the fixed stars. To Dr. Herschel, looking through his celebrated telescope in the direction of the Milky Way, they appeared-to use his own language "scattered in millions like glittering dust;" and their distances from our globe are equally astounding.

a The circumference of a circle is something more than three times the diameter, and, of course, more than six times the semi-diameter. b The sun is more than a million of times larger than the earth, and there is every reason to suppose that each of the fixed stars is a sun!

Light which travels from the sun to the earth in eight minutes —that is, about ninety-five millions of miles in eight minutes— would, it has been computed, be more than three years in coming to us from the nearest fixed star!

Are we to conclude, then, that the sun, and millions upon millions of stars, scattered at all possible distances in the heavens, above, beneath, and around us, revolve round the earth in twenty-four hours, as they appear to do; or that the same effect is produced by a simple rotation of the earth on its axis in the same time? The result, as we have observed before, would, in either case, be the same; but in the one, the means employed would be simple and natural; in the other, complicated, and to our conceptions impossible. We have said nothing of the surpassing magnitudes of the sun and stars compared to that of the earth, and the consequent absurdity of supposing that innumerable large bodies revolve round our globe, which is a mere point when compared to any one of them.

ANNUAL MOTION.

DAY and NIGHT, as we have seen, are produced by the rotation of the earth on its axis from west to east every twenty-four hours. We have now to explain the vicissitudes of the SEASONS. Besides the motion of the earth upon its axis every twenty-four hours, it moves round the sun in the course of a year, in a path nearly circular. The circumference of the circle which the earth describes in moving round the sun is called the earth's ORBIT, and the plain level surface included within, or circumscribed by the orbit, is called the PLANE of the earth's orbit. The word orbit means a circular track or path; and the term plane, a level or plain surface. The circular edge of a round table may represent the orbit of the earth, and the surface of the table its plane. Not that we are to suppose that the orbit of the earth is a solid or substantial ring, or its plane a real, visible, flat surface; for the earth and all the planets perform their evolutions round the sun, with unerring regularity, in pure and pathless space.

a Of the magnitude of the fixed stars nothing is known, except by inference that they are the suns of other systems. Such is their amazing distance, that even when viewed through the most powerful telescopes, they appear, as they do to the naked eye, mere luminous points, their brilliancy only being increased.

To illustrate what has been said, carry a sma globe or ball round a candle in a circular direction, and make it turn, at the same time, round and round, as if upon an axis. These motions given to the ball represent the diurnal and annual motions of the earth. The circumference of the circle described by the centre of the ball in moving round the candle, represents the earth's orbit, and the space which the orbit circumscribes or includes, its plane, The plane, as the term denotes, is in a level or line with the orbit, that is, neither rising above nor sinking below it.

The poles are the extreme northern and southern points of the earth's surface; and if we make the ball spin round, you will observe that the part of it which has the greatest motion is exactly midway between, or equally distant from the poles. Round this part draw a line or circle, and you will have a representation of the equator, which is so called, because it is equally distant from each pole. The equator runs east and west, and divides the globe into the NORTHERN and SOUTHERN HEMISPHERES, or half globes.

Let the small globe or ball, with the poles and the equator marked upon it, be carried round the candle in an erect position, that is, with its axis perpendicular to the plane of its orbit, and it will be evident that the candle will shine directly on the middle or equatorial parts of the ball, and obliquely on the parts in the direction of, and about the poles.

Now, if the earth moved round the sun in this way, that is, with its axis perpendicular to the plane of its orbit, it is easy to conceive that the sun would shine directly on the middle or equatorial parts of it, and obliquely on those parts in the direction of, and about the poles. But if this were the case, there would be no seasons, and consequently, neither animal nor vegetable life in the world. The middle or equatorial parts of the earth would be parched and burned up by their constant exposure to the direct rays of the sun; in the temperate zones, which now enjoy the pleasing vicissitudes of the seasons, there would be perpetual spring-but without the hope of a harvest-while in the polar regions, the rigours of winter would continue unbroken throughout the year.

But the earth does not, as we would think it should, move round the sun in an upright position, but in a slanting direction. The axis, instead of being perpendicular to the plane of its orbit, inclines or leans to it at an angle of 66 degrees;

and as it always points to the same part of the heavens, the northern half of the axis, and consequently the northern hemisphere, will, during one period of the year, incline to, and at another decline from the sun. When the northern half of the axis of the earth is inclined to, the southern will, of course, be declined from the sun; and hence, when it is SUMMER in the northern, it will be WINTER in the southern hemisphere, and vice versa. During two periods of the year the axis of the earth neither inclines to, nor declines from the sun, and the consequence is, that it is neither summer nor winter in either hemisphere. At these periods both hemispheres enjoy an equal degree of light and heat from the sun, and they are called the EQUINOXES-because the night and day are equal all over the world.

To illustrate what has been said-for descriptions, and even diagrams, fail to produce clearness in the minds of children in such matters-let the instructor carry a straight rod or ruler round the edge of a circular table, and let one half of the ruler be above, and the other below the edge of the table. If the ruler is carried round in an erect position, it will be evident to the pupils that it is perpendicular to the surface or plane of the table, and also that it moves parallel to itself, or to the direction in which it was when it commenced to be carried round. But if the ruler be inclined towards the table at an angle of 663 degrees, and made to preserve its parallelism as it is moved round, it will represent the angle made by the axis of the earth with the plane of its orbit, and its inclination towards the sun throughout the year.

As a farther illustration, let the small globe, upon which we marked the poles and equator, be carried round a candle supposed to represent the sun, in the same way as the ruler has been moved round the table, and the causes of the SEASONS will be evident.

[The following familiar illustrations will enable young persons to form clear and correct conceptions of the causes which produce the

SEASONS:

When we sit opposite to a fire, though at a considerable distance from it, we feel the heat more than if we sat close beside it. If the tire is on the floor, or nearly on a level with it, our feet, if sitting near it, will be very warm, while the upper part of our persons may feel cold; but if the fire is raised, say as high as our heads, the heat thrown upon our faces, particularly if we sit opposite to it, will be intolerable; while our feet may not even be warm.