the sun with any point of the earth's equator, it would follow that the north pole, and a certain tract round it, would remain always in the light, notwithstanding the revolution of the earth on its axis. Even those places in the northern hemisphere to which the sun appeared to rise and set, would have their days always longer than their nights; at the equator the days and nights would be equal; but in the southern hemisphere the reverse would happen to what took place in the northern. For those places to which the sun appeared to rise and set would have their nights longer than their days; and the south pole would be constantly in darkness, with a tract around it equal to what was constantly in the light round the north pole. It is evident, also, that in this case the sun would be always on the north side of the equator, and vertical to a certain circle parallel to it, which would be as many degrees from the equator as the angle contained between the earth's axis and the imaginary line wanted of a right angle.

This last supposition is in some degree similar to what actually takes place in nature; for the axis of the earth makes an angle of 23 degrees, with a perpendicular to its orbit; and as the axis always remains parallel to itself, or points in the same direction, this angle must be constantly changing as the earth moves forward in its orbit.*

Some say he bid his angels turn askance
The poles of earth twice ten degrees and more
From the sun's axle; they with labour push'd
Oblique the central globe.

MILTON.

This is well represented by the following figure, which shews the earth in twelve different positions, or at twelve different times of the

The line ab is the equator, n the north pole, and the south, The signs of,, &c. denote the points of the ecliptic in which the earth is when it has the positions in the figure.

*Or, what amounts to the same thing, the axis of the earth makes an angle with the plane of the ecliptic of 66 degrees.

As the position of the poles of the earth, with respect to the sun, depends entirely on this angle, their position must always be changing; and, of course, every point on the earth's surface must also alter its position with respect to the sun. About the 20th of March, when the sun, as seen from the earth, enters the sign Aries, the line supposed to join the centres of the earth and sun is perpendicular to the earth's axis; consequently both poles are similarly situated with respect to the sun, as he is then directly over the equator, and the days and nights are equal at every place on the globe. This time of the year is called the vernal equinox, because spring commences to the inhabitants of the northern hemisphere, while autumn begins to those of the southern.

After the 20th of March the sun appears to rise every day sensibly more to the northward than he did the day before, to be more elevated at mid-day, and to continue longer above the horizon, till the 21st of June, which is the longest day at all places in the northern hemisphere. At this time the angle formed by the northern half of the earth's axis and the line joining the centre of the earth and sun is then at the least, which is 66 degrees. The sun will then appear to touch the tropic of Cancer, and be vertical to all places 23 degrees north of the equator. This time of the year is called the summer solstice, because it is the middle of summer, and the sun seems to remain stationary for a few days.

After the 21st of June, the angle joining the centres of the earth and sun gradually increases, and the sun appears to recede from the tropic of Cancer, in the same manner as he advanced to it, rising every day a little farther to the south than he did the day before, till the 23 of September, when the axis has a similar position to what it had on the 20th of March, being again at right angles to the line just mentioned, consequently the days and nights are again equal all over the globe, which constitutes the autumnal equinox.

The sun now appears to cross the equinoctial, and the south pole which, during the last six months, was in the dark, begins to turn towards the sun; and precisely the same phenomena are exhibited to the southern hemisphere as those already described in the case of the northern half of the earth. On the 22d of December the sun appears to touch the tropic of Capricorn, and is vertical to all those places on the earth that are 231 degrees south of the equator. The days are then longest at all places in the southern hemisphere, but at the shortest in the northern. This time of the year is termed the winter solstice.

From the tropic of Capricorn the sun again appears to move forward, and to arrive at the equinoctial again on the 20th of March. Thus by a combination of the annual and diurnal motions of the earth, with the parallelism of its axis, and the obliquity of its orbit to the plane of its equator, the various seasons are produced, and the same quantity of light and darkness, in the space of a year, are distributed to every region of the globe.

The manner in which the sun enlightens the earth, the parallelism of its axis, and the increase and decrease of the days and nights,

may be well illustrated by a small terrestrial globe, suspended by a string fastened to its north pole, as represented by the following figure.

A circle of wire a b, representing the plane of the earth's equator, may be held parallel to a table, and equal in height with the flame of a candle standing upon it. If the string be twisted a little towards the left hand, and the globe suspended within the circle, with its equator at the same height, the globe will begin to turn on its axis from west to east, and day and night will be represented by the light and shade produced by the candle on its surface. But if the globe be carried round the wire, to represent a year, the candle will illuminate both poles, and every spot on its surface will describe half a circle in the enlightened part, and half in the dark part, and make equality of day and night through the year. This is, however, not the case in nature, as has already been fully explained. If then the wire be inclined to the table at an angle of 23 degrees, as represented by the circle a bed, and the globe be carried gently round it, the seasons, and increase of day and night, will appear as they are in nature; i. e. when the globe is at a, the candle enlightens it no farther northward than the arctic circle no; all within which, in the middle of our winter, is deprived of a sight of the sun; while all places within the antarctic, or opposite circle, have perpetual day: at this time the candle shines verticaily on the tropic of Capricorn. As the earth moves towards b (the vernal equinox), if a small patch be laid on latitade 5140 north, it will shew how the days increase at London, and how the nights decrease. When it has arrived at b, the candle will then be perpendicularly over the equator, and, shining to both poles, equality of day and night will take place: as it proceeds towards e(the summer solstice), the days increase, and the candle shines more and more over the north pole: when it has arrived at e,

the whole arctic circle, and the countries it includes, will revolve in continual sight of the sun; and all within the antarctic circle will be deprived of that sight. At this time the candle shines vertically on the tropic of Cancer. Moving from midsummer towards d (the autumnal equinox), the days will be found to decrease, and the nights to increase in length, till they come again to equality at d, and thence to the winter solstice, and so on.

The particular temperature which distinguishes each of the seasons, at any paiticular place, is owing to a difference in the sun's altitude, and the time of his continuance above the horizon of that place. In winter, the rays of the sun fall so obliquely, and the sun is such a short time above the horizon, that his influence in heating the earth is but very little, compared with what it is in summer. For at this

season, the sun is so much higher than in winter, that his rays not only fall more perpendicularly, but more of them fall on any given space; and as the day is also much longer than the night, the temperature of the earth and the surrounding atmosphere must be much greater than in winter.

Since the power of the sun is greater in heating the earth at any particular place, when his rays fall most directly, and when the days are longest at that place, it may be asked, how does it happen that the heat is greatest about the end of July, when the sun is highest and the day longest about the 21st of June? The reason of this may easily be discovered by attending a little to the manner in which bodies are heated. The heat which the earth receives is not transient, but is retained by it for some time. For, like other solid bodies, it receives heat and parts with it gradually. Now as the earth continues to receive more heat in the day than it gives out in the night, for a considerable time after the 21st of June, its temperature will continue to increase, till the days and nights begin to approach to an equality. But this is not the case till the end of July, at least; the earth goes on increasing in temperature, till about this time, when it is found to be much greater than about the 21st of June, although the sun be then higher at mid-day, and the day longer than at any other time of the year in the northern hemisphere. The heat in July would be still greater were the sun at his mean distance from the earth; but this is not the case, for he is then at his greatest distance. However, the difference between his distance at this time and the mean distance being only 4th part of the whole, it could not make a great alteration in the heating power of the rays. But if it does operate in any degree in diminishing the heat in the northern hemisphere in July, the same cause must operate in increasing the heat, but in a double degree, in the southern hemisphere in January. For the sun is th part nearer the earth than his mean distance on the 1st of January. Consequently the heat must be greater in the southern hemisphere in January than in the northern in July, all other circumstances being the same. The effects of the direct in

*The same phenomena take place in the southern hemisphere in a reverse order, or at six months' difference of time.

fluence of the sun are, however, greatly modified by the transportation of the temperature of one region into another, in consequence of that disturbance in the equilibrium of the atmosphere which the action of the sun's rays necessarily produce.

Thus we see by what simple means the whole variety of the seasons are produced; and also how admirably fitted the means are to accomplish the end.

These, as they change, Almighty Father, these
Are but the varied God. The rolling year
Is full of Thee. Forth in the pleasing Spring
Thy beauty walks, Thy tenderness and love.
Wide flush the fields; the softening air is balm;
Echo the mountains round; the forest smiles;
And every sense, and every heart is joy.
Then comes Thy glory in the Summer months,
With light and heat refulgent. Then Thy sun
Shoots full perfection through the swelling year:
And oft Thy voice in dreadful thunder speaks;
And oft at dawn, deep noon, or falling eve,
By brooks, and groves, in hollow-whispering gales.
Thy bounty shines in Autumn unconfin'd,
And spreads a common feast for all that lives.
In Winter awful Thou! with clouds and storms
Around Thee thrown, tempest o'er tempest roll'd,
Majestic darkness! on the whirlwind's wing,
Riding sublime! Thou bidst the world adore.

ON THE REGULATION OF TIME BY THE HEAVENLY BODIES.

Time of itself is nothing, but from thought
Receives its rise; by labouring fancy wrought
From things considered, while we think on some
As present, some as past, or yet to come.

No thought can think on time that's still confest,
But thinks on things in motion or at rest.

Though time, considered in an abstract and philosophical point of view, was certainly coeval with the Deity, since nothing can possibly exist but in some portion of it, yet the measuring of time is a matter of a very different nature; and though various nations have differed on this subject, it is, nevertheless, a subject of the utmost importance to every human being. For the opposite and contradictory methods of calculating time have often been productive of very great mischief in the world; while chronologers, sometimes from ignorance, and as often from prejudice, have misrepresented events, which, however trifling they might appear to them, may nevertheless affect the happiness of future ages. During the general chaos, or that period when the materials of which the beautiful fabric of the universe was what Ovid calls rudis indigestaque moles, a rude and indigested heap, there were no human beings, and consequently no occasion for any method of measuring or regulating time. But as