It is wonderful that the sea, which has a natural disposition, from its being a purer and lighter element, to be above the earth, should not overflow it; but the amazing power of Omnipotence retains it within its prescribed limits. For he has pronounced, “Hitherto shalt thou come, but no further; and here shall thy proud waves be stayed.” As if he had said, Though thy tides flow with mighty strength, though the swelling billows of thy pride (so the original) rise high in a storm, and dash against the shore with impetuous force and overwhelming rage, yet here shall they stop: though they roar and foam, as if irritated at the opposing strand, yet dare not to approach beyond those limits to thee assigned; but, obedient to thy Lord and Master, submissively retire. Here we see the power and dominion of the supreme Being in the kingdom of nature, whose sway the sea is subject to! Our preservation from its threatening destruction, by the continual restrictions it is under, is a perpetual expression of Divine goodness and mercy, and should induce all men to live always in the reverential fear of God. “Fear ye not me? saith the Lord: will ye not tremble at my presence, which have placed the sand for the bound of the sea, by a perpetual decree, that it cannot pass; and though the waters thereof toss themselves, yet they cannot pass over it.”
If we look upon the map of the world, we shall find that the ocean occupies a considerably greater surface of the globe than the land is found to do. Although the ocean, properly speaking, is but one extensive sheet of water, continued over every part of the globe without interruption; and although no part is divided from the rest, yet geographers have distinguished it by different names, as the Atlantic or Western Ocean; the Northern, Southern, Pacific, Indian, and German Oceans. In this vast receptacle, almost all the rivers of the earth ultimately terminate. And yet these vast and inexhaustable supplies do not seem to increase its stores; for it is neither apparently swelled by their tribute, nor diminished by their failure; it continues constantly the same. Indeed, the quantity of water of all the rivers and lakes in the world is nothing compared to that contained in this prodigious reservoir. And some natural philosophers have carried their ideas on this subject so far as to assert, in consequence of certain calculations, that, if the bed of the sea were empty, all the rivers of the world flowing into it with a continuance of their present stores, would take up at least 800 years to fill it again to its present height.[75]
To ascertain the depth of the sea has been found impracticable, both on account of the numerous experiments which it would be found necessary to make, and the want of proper instruments for that purpose. Beyond a certain depth the sea has hitherto been found unfathomable; and though several methods have been contrived to obviate this difficulty, none of them has completely answered the purpose. We know in general that the depth of the sea increases gradually as we leave the shore; but if this continued beyond a certain distance, the depth in the middle of the ocean would be prodigious. Indeed, the numerous islands every where scattered in the sea demonstrate the contrary, by showing us that the bottom of the water is unequal like the land, and that so far from uniformly sinking, it sometimes rises into lofty mountains. If the depth of the sea be in proportion to the elevation of the land, as has been generally supposed, its greatest depth will not exceed five or six miles; for there is no mountain six miles perpendicular above the level of the sea. The sea has never been actually sounded to a greater depth than a mile and 66 feet; every thing beyond that, therefore, rests entirely upon conjecture and analogical reasoning, which, in this case, are in no wise conclusive. Along the coasts, where the depth of the sea is generally well known, it has always been found proportioned to the height of the shore; when the coast is high and mountainous, the sea that washes it is deep; when, on the contrary, the coast is low, the water is shallow. Whether this analogy holds at a distance from the shore, experiments alone can determine.
Water is an uninflammable fluid, says Dr. O. Gregory, and, when pure, is transparent, colorless, and void of taste and smell. Mr. Cavendish made a discovery that it is formed by the union of hydrogen and oxygen. It may, therefore, be considered as oxide of hydrogen: oxygen and hydrogen appearing to unite, only in that certain proportion of which water is the result. In 1798, (observes Mr. Parkes) Mr. Sequin made a grand experiment for the composition of water. He expended no less than 25,582 cubic inches (or nearly two hogsheads) of inflammable air, and 12,457 of vital air. The first weighed 1,039 grains, and the second 6,210, amounting to 7,249 grains, and the water obtained amounted to 7,245 grains, or about three-fourths of a wine pint. The loss was only four grains. Another experiment was afterwards made by Le Fevre, in which nearly two pounds and a quarter of water was produced.
The sea water contains a quantity of salt, but not in the same proportions every where. In the torrid zone, where otherwise, from the excessive heat, it would be in danger of putrefaction, the water is found most salt; as we advance northward its briny quality diminishes, till at the poles it is nearly gone altogether. Under the line, Lucas found that the sea comprised a seventh part of solid contents, consisting chiefly of sea-salt. At Harwich, he found it yielded 1-25 of the same matter. At Carlscroon, in Sweden, it contains 1-30 part, and on the coast of Greenland a great deal less. This gradual diminution of saltness from the equator to the pole, is not, however, without particular exceptions. The Mediterranean sea contain 1-22 of the sea-salt, which is less than the German sea contains. The saltness of some seas, or of particular parts of the same seas, may be increased, as Mr. Boyle intimates, from rocks and other masses of salt, either at the bottom of the sea, or dispersed near their shores.
This phenomenon of the sea perplexed the philosophers before the time of Aristotle, and surpassed even the great genius of that philosopher. Father Kircher, after having consulted three and thirty authors upon the subject, could not help remarking, that the fluctuations of the ocean itself were scarcely more various than the opinions concerning the origin of its saline impregnation. Bernadine Gomesins, (observes Bishop Watson) about 200 years ago, published an ingenious treatise on salt: in this treatise, after reciting and refuting the opinions of Empedocles, Anaxagoras, and Aristotle, on the subject in question, he proposes his own; wherein he maintains, that the sea was originally created in the same state in which we at present find it, and impregnated, from the very first, with the salt which it contains. Indeed, we cannot account for the general saltness of the sea from second causes; hence we must suppose it has had this property from the creation. Naturalists assure us, that, though some few species of fishes thrive in fresh water, and some others live alternately in fresh and salt, yet by far the greatest number cannot exist out of the sea; which is a proof that the sea was at the creation impregnated with salt.
The saltness of the sea has been considered by some as a peculiar blessing from Providence, in order to keep so great an element pure and wholesome: but facts prove that this property is not capable of preserving it from putrefaction. Sir Robert Hawkins, one of our most enlightened navigators, gives an account of a calm, in which the sea continuing for some time without its usual motion, began to assume a very formidable appearance. “Were it not (says he) for the moving of the sea, by the force of winds, tides, and currents, it would corrupt all the world. The experiment of this I saw in the year 1590, lying with a fleet about the islands of Azores, almost six months; the greatest part of the which time we were becalmed. Upon which all the sea became so replenished with various sorts of gelies, and forms of serpents, adders, and snakes, as seemed wonderful; some green, some black, some yellow, some white, some of divers colors, and many of them had life; and some there were a yard and a half and two yards long; which had I not seen, I could hardly have believed. And hereof are witnesses all the companies of the ships which were then present; so that hardly a man could draw a bucket of water clear of some corruption. In which voyage, towards the end thereof, many of every ship fell sick, and began to die apace. But the speedy passage into our country was a remedy to the crazed, and a preservative for those that were not touched.”[76] Mr. Boyle informs us, that he once kept a quantity of sea water, taken from the English channel, for some time barrelled up; and, in a few weeks, it began to acquire a fetid smell. He was also assured by one of his acquaintance, who had been becalmed for about fourteen days in the Indian ocean, that the water, for want of motion, began to stink; and, that had the calm continued much longer, the stench would probably have poisoned him. It is the motion, therefore, and not the saltness of the sea, that preserves it in its present state of salubrity.[77]
The sea has three kinds of motion: the first is that undulation which is occasioned by the wind. This motion is evidently confined to the surface; the bottom, even during the most violent storms, remains perfectly calm. Mr. Boyle has remarked, from the testimony of several divers, that the sea is affected by the winds to the depth only of six feet. It would follow from this, that the height of the waves above the surface does not exceed six feet; and that this holds, in the Mediterranean sea at least, we are informed by the Compte de Marsigli; though he also sometimes observed them, during a very violent tempest, rise two feet higher.
The second kind of motion is that continual tendency which the whole water in the sea has towards the west. It is greater near the equator than about the poles; and, indeed, cannot be said to take place at all in the northern hemisphere beyond the tropic. It begins on the west side of America, where it is moderate; hence that part of the ocean has been called Pacific. As the waters advance westward, their motion is accelerated; so that, after having traversed the globe, they strike with great violence on the eastern shore of America. Being stopped by that continent, they turn northward, and run with considerable impetuosity in the Gulf of Mexico; from thence they proceed along the coast of North America, till they come to the south side of the great bank of Newfoundland, when they turn off, and run down to the Western Isles. This current is called the Gulf stream. It was first accurately described by Dr. Franklin, who remarked also, that the water in it having been originally heated in the torrid zone, cools so gradually in its passage northward, that even the latitude might be found in any part of the stream by means of a thermometer. This motion of the sea westward has never been explained: it seems to have some connection with the trade-winds, and the diurnal revolution of the earth upon its axis.
The third, and most remarkable motion of the sea, is the tide; which is a regular swell of the ocean every 12 hours, accounted for from the principal of gravitation. The sagacious Kepler long ago conjectured, that the earth and moon, and every particle of them, mutually gravitate towards each other, and are the cause of the tides. If, says he, the earth ceased to attract its waters towards itself, all the water in the ocean would rise and flow into the moon: the sphere of the moon’s attraction extends to our earth, and draws up the water. This, at that time, was mere conjecture; for Sir Isaac Newton was the first who clearly pointed out the cause of this phenomenon. On the shores of the ocean, and in bays, creeks, and harbors, which communicate freely with it, the waters rise above their mean height twice a day, and as often sink below it, forming what is called a flood and an ebb, a high and low water. It has been stated, that in the middle of the sea the tide seldom rises higher than one or two feet; but, on the coast, it frequently reaches to the height of 45 feet, and, in some places, even to more. At Plymouth, it is sometimes 21 feet between the greatest and least depth of the water in the same day, and sometimes only 12 feet.