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a. THE OCEAN.-Let us observe in this connection,

a1. The sea-breeze.

§ 46. To render a tropical country habitable, or at least to preserve in it health and comfort, what design would we, a priori, consider better than the periodical introduction of a breeze whose coolness and whose strength would relieve the heat of noon? Now this is what the sea-breeze does. The more tropical the climate, the more regular its approach and the more steady its continuance. "Usually," says Mr. Gosse, when speaking of the tropics, "about the hour of ten in the forenoon, when the heat of the sun begins to be oppressive, a breeze from the sea springs up, invigorating and refreshing the body by its delightful coolness, and continues to blow through the whole day, gradually dying away as the sun sinks to the horizon. Then about eight in the evening, an air blows off the land until near sunrise; but this is somewhat variable and irregular, always fainter than the sea-breeze, and dependent on the proximity of mountains. The application of what has been already said of the causes of wind in general will be readily made to these particular cases, the air on the surface of the water being cooler during the day, and that on the mountains during the night. Either is a grateful alleviation of the oppressive sultriness of the climate."* To this may be added the peculiarly refreshing qualities of the salt with which the sea-breeze is freighted.

b1. The ocean salts.

§ 47. Three things we would suppose necessary, a priori,

* Gosse, on the Ocean, p. 31.

in such a body as the ocean: first, such superior lightness as will make it a fit medium for the commerce of the world; secondly, such an amount of mobility and circulation as will afford highways for travel, as well as a preservative agency to the sea itself; thirdly, the material from which those numberless tribes by which the deep is thronged, may construct their homes. Now in view of such a design, what could be more effective than the salts by which the ocean is permeated? By them the specific gravity of the water is so far increased as to add materially to the buoyancy of whatever solids are placed in it. And the compensations by which this quality is maintained are no less worthy of notice. If a similar solution was placed in a vessel exposed to the sun, there would soon be little left besides a dry saline crust. But by a most delicate adjustment of the exquisite accuracy of which science can best judge by the results, the water evaporated by the sun is so far restored by the rivers as to retain throughout the vast volume the same specific gravity and the same saline admixture.

These salts contribute largely to that great system of oceanic circulation on which commerce so much depends. Fresh water is but feebly affected by the dynamical impulses set on foot by changes of temperature; salt water, through its peculiar contraction as its temperature lowers, is so agitated as to produce those great currents which form the ocean railways. From this we have a "surface current of saltish water from the poles toward the equator, and an under current of water salter and heavier from the equator to the poles. This under current supplies, in a great measure,

the salt which the upper current, freighted with fresh water from the clouds and rivers, carries back. Thus it is to the salts of the seas that we owe that feature in the system of oceanic circulation which causes an under current to flow from the Mediterranean into the Atlantic, and another from the Red Sea into the Indian Ocean. Hence, too, we infer that the transportation of warm water from the equator toward the frozen regions of the poles, is facilitated; and consequently here, in the saltness of the sea, have we not an agent by which climates are mitigated-by which they are softened and rendered more salubrious than it would be possible for them to be were the waters of the ocean deprived of their property of saltness?"*

§ 48. To the salts, but more particularly to the solutions of lime which the fresh water streams pour into the ocean in such large amounts, we owe another very important element in the marine economy. It is here that the little builders of the ocean find the quarries from which their houses are constructed. Hence come the stone and the mortar which is worked into the creviceless dome which rises over the oyster's home. Hence come the minarets which form at once the guards and the ornaments of one species, and the peaked spear-heads which strengthen the armor of another. Here it is that the masons of the coral bank find their stone. When we recollect the myriads of creatures whose happiness is promoted and whose life secured by this process, we may well, as we look at the limestone rivulet that washes

* Maury, Phys. Geog. of the Sea, % 316, &c.

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the mountain side, admire the wisdom and goodness by which its ingredients are composed and its course is directed. For it goes to aid in building innumerable cities to be inhabited by an active and useful population,—a population whose members not only subserve their immediate end as parts of the great chain of created beings, but perform an important office in maintaining that balance of life without which man himself would cease to exist.

"How

For by them is no small part of the great work of the movement of the waters carried on. We all know in how short a time a comparatively small body of insects—the soldier-ant, for instance-is capable of undermining a solid wall. But here, in an element in a vast degree more susceptible to their subtle action, we have myriads upon myriads of artificers at work. Thither they proceed, these hod-men of the seas, carrying away from its ocean beds their countless little loads of mortar, of salts, and of solids. much solid matter," says the same intelligent observer whom we have just quoted, "does the whole host of marine plants and animals abstract from sea water daily? Is it a thousand pounds, or a thousand millions of tons? No one can say. But whatever be its weight, it is so much of the power of gravity applied to the dynamical forces of the ocean. And this power is derived from the salts of the sea, through the agency of sea-shells and other marine animals. Yet they have power to put the whole sea in motion, from the equator to the poles, and from top to bottom."

c1. The Gulf Stream.

§ 49. Assuming, at the outset, the division of the earth

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into zones, of such a character as to generate variety of produce and of character, and hereby to promote enterprise, both in commerce and in productive industry, it must follow, that large sections, unless some compensatory process be adopted, will be so far removed from the mean temperature as to be unsuitable for human habitation. Thus, without some such process, England, Norway, Sweden, and even the north of France, would be desolated on the one side by cold, and the islands of the Caribbean Sea, and the countries bordering on the Gulf of Mexico, by heat. What process would we suppose an intelligent and beneficent Creator to adopt to equalize these extremes, by drawing from the one to the other the excess of heat, and by throwing back the excess of cold?

Now, before we answer this question, let us suppose that we visit, in the dead of winter, one of the larger and more complete hot-houses, by which the vegetables and fruits of summer are brought to the market in early spring. There, where all the skill of recent experience is brought to bear, we will find, in a cellar under an out-house, a large boiler, in which water is heated. From this pipes are taken to a chamber, where they are so flared out as to raise to a high degree of heat a given body of air, which is afterwards taken by a hot air-pipe to the green-house. The water, being cooled, is collected again in a single pipe, and thus returned to the boiler to be re-heated. Again the circuit is commenced, and again completed, and so on until the desired temperature is reached. So it is, that, by a very simple and yet beautiful apparatus, the climate of summer

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