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tive mind perceives a dreary uniformity in all around, the penetrating eye of the rural student discovers many a varied aspect of beauty and excellency, which still invite to the most pleasing investigation. And, however paradoxical it may appear, he finds inexhaustible sources of serenity and delight, in that mood of melancholy musing on scenes of desolation, which, in vulgar estimari tion, would rather
Deepen the murmur of the falling floods,
In fine, in each vicissitude of the seasons, he still discerns the omnipotent Creator, ever bountiful to man; and, whether the gentle gales breathe propitious in spring, or resistless storms ravage the earth in winter, his cultivated mind kindles with devotion, and even calls upon the inanimate world to join him in adoration:
To him, ye vocal gales,
In the subject of my preceding essay, I had a satisfaction in exhibiting some of those admirable pictures, which the great poets and painters of Nature have been found to trace. I next entered, with the natural philosopher, into a disquisition concerning those wonderful vestiges of beauty and usefulness, of wisdom and contrivance, which not only demonstrate a Creating Hand, but demonstrate that Hand to be Divine. “And finaily, with the religious and sentimental reader, I indulged
such moral reflections as the subject had a tendency to inspire. This is the order, which, once for all, I mean to pursue in my future lucubrations, and by which I hope to gratify alike the poet, the philosopher, and the christian
The subject, hitherto, has been chiefly confined to what the surrounding country affords; but we are now carried to the distant ocean.
Wide o'er the moving wilderness of waves,
Virgil, in the first book of his Æneid, gives the description of a storm, which, as Mr. Spence observes, probably set all the Roman poets a stormpainting. Thomson also gives a minute and picturesque description, with circumstances more natural to the English reader, especially in the various passages that announce the approaching tempest',
To account, philosophically, for the cause of winds, we must have recourse to the elasticity of the air, that property which renders it capable of compression and expansion. This elasticity is increased by heat, which rarefies and expands the air; and of this property, the wind is a necessary consequence: for, when the atmosphere is heated over one part of the earth more than over another, the warmer air, in this case, being rarefied, becomes specifically lighter than the rest. It is therefore overpoised by it, and raised upward; the upper parts of it diffusing themselves every way over the top of the atmosphere; while the neighbouring inferior air rushes in from all parts at the bottom; which it continues to do, till the equilibrium is restored. Upon this principle it is that most of the winds may be accounted for. Hence, moreover, we may account for the rushing of the
* See his Winter, line 118 to 201.
air into a glasshouse, or toward any place where a great fire is made; for the ascending of smoke up a chimney; and for a circumstance so little attended to, as the rushing of the air through the keyhole of a door, or any small chink, when there is a fire in the room.
Nor is this mere speculation, or conjecture: for the truth of this general observation, that the air will press toward that part of the world where it is most heated, has been demonstrated beyond any kind of doubt, by the following very simple experiment. Fill a large dish with cold water : into the middle of this put a waterplate filled with warm water.
The first may represent the ocean, and the other an island rarefying the air about it. Blow out a wax candle, and if the place be still, on applying it successively to every side of the dish, the smoke will be seen to move toward the plate. Again, if the ambient water be warmed, and the plate filled with cold water, let the smoking wick of the candle be held over the plate, and the very reverse will happen.
Under the equator, the wind is always observed to blow from the east point. For, supposing the sun to continue vertical over some one place, the air will be most rarefied there; and, consequently, the neighbouring air will rush in from every quarter with equal force. But, as the Sun is continually shifting to the westward, the part where the air is most rarefied is carried the same way; and therefore the tendency of all the lower air, taken together, is greater that way than any other. Thus the tendency of the air toward the west becomes general; and its parts impelling one another, and continuing to move till the next return of the sun, so much of its motion as was lost by his absence is again restored; and, therefore, the easterly wind becomes perpetual. On each side of the equator, to about the 30th
degree of latitude, the wind is found to vary from the east point, so as to become northeast on the northern side, and south-east on the southern. The reason of this is, that, as the equatorial parts, are hotter than any other, both the northern and southern air ought to have a tendency that way; the northern current, therefore, meeting in this passage with the eastern, produces a north-east wind on that side; as the southern current joining with the same, on the other side of the equator, forms a south-east wind there.
This is to be understood of open seas, and of such parts of them as are distant from the land ; for near the shores, where the neighbouring air is much rarefied, by the reflection of the sun's heat from the land, it frequently happens otherwise; particularly on the coast of Guinea, where the wind always sets in upon the land, blowing westerly instead of easterly. This is occasioned by the deserts of Africa, which lying near the equator, and having a very sandy soil, reflect a greater degree of beat into the air above them; which being thus rendered lighter than the air which is over the sea, the wind continually rushes in upon the land, to restore the equilibrium.
That part of the ocean which is called the Rains, is attended with perpetual calms, the wind scarcely blowing sensibly either one way or the other. For this tract being placed between the westerly wind blowing from the ocean toward the coast of Guinea, and the easterly wind blowing from the same coast to the westward thereof, the air stands in equilibrium between both ; and its gravity is so much diminished thereby, that it is not able to support the vapour it contains, but lets it fall in con tinual rain; and hence this part of the ocean rem ceives its name.
There is a species of winds observable in some
places between the tropics, called Monsoons, or Trade Winds, which, during six months of the year, blow one way, and the remaining six the contrary. The cause of them, in general, is this: when the sun approaches the northern tropic, there are several countries, as Arabia, Persia, India, &c. which become hotter, and reflect more heat than the seas beyond the equator, which the sun has left; the winds, therefore, instead of blowing thence to the parts under the equator, blow the contrary way; and when the sun leaves those countries, and draws near the other tropic, thie winds turn about, and blow on the opposite point of the compass.
From the solution of the general trade winds, we may see the reason why, in the Atlantic ocean, a little on this side the 30th degree of north latitude, there is generally a west or south-west wind. For, as the inferior air within the limits of those winds is constantly rushing toward the equator, from the north-east point, or nearly so, the superior air moves the contrary way; and, therefore, after it has reached these limits, and meets with air, that has little or no tendency to any one point more than to another, it will determine this air to move in the same direction with itself.
In our own climate we frequently experience, in calm weather, gentle breezes blowing from the sea to the land, in the heat of the day which phenomenon is very agreeable to the principle laid down above: for the inferior air over the land being rarefied by the beams of the sun reflected from its surface, more than that which impends over the water, the latter is constantly moving on to the shore, in order to restore the equilibrium, when not disturbed by stronger winds from another quarter. And hence, in hot countries, the sea breezes almost invariably blow from sea to land, in the