to them, and obliquely, and therefore less powerfully, upon all other parts of its convex surface, till, at the extremes of the hemisphere, they would entirely cease to reach the earth. Were the earth stationary, therefore, the consequence of its globular form would be, that the sun-would shine intensely and constantly on a single spot, while one-half of its surface would be left in total darkness, and the other would be illuminated with greater or less force, according to its distance from the sun's direct rays. The disadvantages of such an arrangement need no comment. Now, one way in which this evil is abated, is by what is called the diurnal rotation of the earth. Our globe is made to whirl round as on two pivots, which are called the poles* of the earth, once in twenty-four hours. This, while it causes the grateful alternation of day and night, conveys light and heat round the world, so as to diffuse them with nearly equal force on every spot within the same parallel of latitude. Were the earth in the form of a cylinder or roller, this rotatory motion would cause the sun, in the course of the annual revolution, to shine equally on every part of its round surface, while his rays would never reach the wide flat regions at either end; the days and nights would then be invariably of the same length; there would be no change of climate, and all the habitable parts of the earth would be one burning tropical region, without abatement and without variety. If, on the other hand, the earth, in its present form of a ball, were to have no yearly as well as daily motion, or, having an yearly motion, were to move round its own axis in what may be considered the most simple manner, that is, in an erect position with reference to the sun, the effect. would be, that he would constantly shine with his di-, rect rays only on that single line of the earth's surface which is called the equator. There would still be no

*The extended line through the centre of the globe, on which it turns, is called the axis of the earth,-taking the metaphor from the axis of carriage wheels.

change of seasons, and the accumulated heat in the equatorial regions would be so excessive, as to destroy, in all probability, both animal and vegetable life; while, in the neighbourhood of the polar circle, and even in a vast extent of those countries to which we now give the name of temperate, the globe would be uninhabitable, from the contrary cause of extreme and uniform cold.

The contrivance, by which this inconvenience is, to a desirable extent, removed, is well known. The earth, which, in common with the other planets, performs an annual revolution round the sun, is made to take this course, not in an erect, but in an inclined position; by which means the pole, which leant toward the sun in one part of the course, leans away from it in another. The consequence of this is, that the sun, instead of shining constantly with his direct rays upon the equator, appears to be continually traversing a considerable space in the heavens, shifting from tropic to tropic, and presenting himself for one half of the year to the north, and for the other half to the south of the equator. The various parts of the earth's surface, within the tropics, are thus exposed alternately to the direct and indirect rays of the sun at different periods, and the position and influence of this source of light and heat, is also varied oyer the whole globe, or, in common language, the diversified appearances of the seasons are produced.

This is a most beneficial arrangement; but it is evident that it could only be salutary within a certain range, for this simple reason, that, were the sun to traverse from pole to pole, it would necessarily happen, that while he was shining vertically on the south pole, the north would be left to total darkness, and the tenfold rigours of a polar winter; and, vice versa, while he was pouring the unmitigated radiance of his burning rays on the regions of the north, the south would be doomed to undergo the extreme, which, a few months before, had carried desolation to the north. The fatal consequences of this need not be described; the whole

balance of nature, at present so nicely adjusted, would be upset, the elements would be in constant and furious commotion, and no organized existence, such, at least, as is at present to be found on the earth, could survive the conflict; or, if it did, could endure the violent changes of the seasons, for a single year.

It would be by no means difficult to prove, that the extent to which the range of the sun is actually confined, is precisely that which manifests the most consummate intelligence in the great Artificer. Had it been either more or less than we actually find it, the same advantages would not have been secured, other things remaining as they are, nor would inconveniences have been so effectually avoided. Evils, indeed, still remain ; it is part of the system of a world of discipline that it should be so, but the proof of Divine contrivance lies in this, that these evils are at the minimum, while the advantages, on the contrary, are at the maximum; that is to say, that any alteration either way would be for the worse. Here, then, we have, what we are taught to look for by the general analogy of nature, a proof of supreme wisdom in the adjustment of materials,-the adaptation of means with admirable skill to a beneficent end.

FIRST WEEK-THURSDAY.

CIRCULATION IN THE ATMOSPHERE AND OCEAN.

We have mentioned the inclination of the earth's axis to the plane of its annual orbit, as the cause of the variety of seasons on its surface; but there are other beneficial arrangements which concur with, and are influenced by this, and without which it would but imperfectly secure what is obviously the main design of the Creator, namely, the furnishing of an extensive and varied surface, fit for the habitation of living creatures, and especially of man, the only creature endowed with the higher

attributes of reason, and therefore a subject of moral discipline. Among these arrangements we shall, in the present paper, only allude to the circulation established in the fluid elements which surround our globe.

The expansion of fluid substances by heat, and their contraction, within certain bounds, by cold, is a universal law of nature. Now, this law has an obvious tendency to create circulation. The fluid becoming lighter by being expanded, and heavier when contracted, rises towards the surface, or falls towards the bottom, in proportion to the partial application of heat or cold, and thus tends to diffuse an equable temperature through the whole mass. But this principle has also another effect, which we have more immediately in view. When the fluid expands, it occupies a greater space, and must therefore displace some of the mass with which it is surrounded; when it is contracted, the contrary effect follows,-its diminished bulk is supplied by the rushing in of the contiguous fluid. In either case a current is created.

In regarding the effects thus produced on the atmosphere, it is scarcely possible not to recognize the impress of wisdom and goodness. It is to this cause, operating on the combined air and vapour, that we owe alternate clouds and sunshine, winds and calms, drought, moisture, and rain, every thing, in short, that we call weather,the changes of which are so essential to the fertility of the earth and salubrity of the climate. But, in the midst of these alternations, there is another and more extensive operation constantly going on. The atmosphere, heated and expanded at the equator, is continually flowing in the upper regions towards the poles, where, being cooled and contracted, it acquires a retrograde motion, and flows back in a perpetual under-current towards the equator. This, at least, is its general bias, happily modified, however, by various circumstances and disturbing forces, which retard, divert, and mingle the opposing currents; and while they reduce the temperature of the one, increase that of the other. This, then, is one of

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those providential contrivances by which the fervid heat of the torrid zone is alleviated, and the excessive rigour of the polar regions is subdued, while the intervening temperate climates are rendered more salubrious, and the wide extent of earth is prepared for the comfortable sustenance of animal life.

A similar effect is produced by the movements of the ocean. The expanded waters of the equatorial circle rush towards the poles, carrying with them some of the warmth of those burning regions, which they perpetually pour into the atmosphere of the temperate and frigid divisions of the earth; while the chilled and contracted waters of the extreme north and south, throw back their currents upon the tropics, and thus, in their turn, modify the temperature in these latter climates. In our own quarter of the globe, we observe this effect exemplified in what is called the Gulf-stream of the Atlantic, which is a perpetual current,-occasioned partly by the law already alluded to, and partly by the form of the African and American coasts,-running from the northern shore of South America, where the heat is at its maximum, along the coast of the United States, sweeping across from Newfoundland to the Icy Sea, enveloping the British islands, and thence returning along the shores of France, Spain, and Africa, till it completes its circuit by again reaching the southern continent of America and the Western Indies. That the effect which might be anticipated from this circulation is actually produced, we have a proof in the comparative mildness of the temperature in insular countries. The climate of Great Britain, for example, is more equable than that of the adjoining continent, being considerably cooler in summer, and warmer in winter.

"Great as the difference of temperature is in different climates," says Whewell, “it would be still greater if there were not this equalizing and moderating power exerted constantly over the whole surface. Without this influence, it is probable that the two polar portions