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Saltness of the Sea

ledge would have served as a clue to direct us to a full investigation of this matter in general; but it is to be regretted, that no such observations have, till very lately, been made with any tolerable precision. - There are three principal opinions on this subject, which have been maintained by philosophers of modern date; some, observing that river water, almost in every part of the globe, is in a greater or less degree impregnated with sea salt, have thought that the sea has gradually acquired its present quality of salt from the long-continued influx of rivers.

Other philosophers, observing that large beds of fossil salt are not unfrequent in any quarter of the globe; and conceiving, with great probability, the bottom of the sea to be analogous in its formation to the surface of the earth, have undertaken to derive its saltness from the beds of rock salt, which they have supposed to be situated at its bottom; and they are further of opinion, that without such a permanent saline principle, the sea would long since have become insipid from the fresh water poured into it by an infinity of rivers. Strange! that what, according to the fore-mentioned hypothesis, was thought sufficient to account for the saltness of the sea, should in this be esteemed instrumental in annihilating the saltness already supposed to exist. Boyle unites, as it were, and takes the two preceding hypotheses, and imagines the saltness of the sea to be supplied, not only from rocks and other masses of salt, which at the beginning were, and in some countries may yet be found, either at the bottom of the sea, or at the sides, where the water can reach them, but also from the salt which the rivers, rains, and other waters, dissolve in their passage through divers parts of the earth, and at length carry with them into the sea. Buffon, and the generality of philosophers, acquiesce in the opinion of Boyle." After all, (says he,) it may be observed, that we are inquiring into the cause of a phenomenon, which it may be said had no secondary cause at all. It is taken for granted, in this disquisition, that the water which covered the globe in its chaotic state, was not impregnated with salt as at present, but quite fresh: now this is an opinion concerning a matter of fact, which can never be proved either way; and surely we extend our speculations very far, when we attempt to explain a phenomenon, primeval to, or coeval with, the formation of the earth."

This sensible writer then states the different experiments which have been made to discover the saltness of the sea, round the shores of Britain; and proposes the following simple method of ascertaining it with tolerable certainty :- "As it is not every person who can make himself expert in the use of common means of estimating the quantity of salt contained in sea water, I will mention a method of doing it, which is so easy and simple, that every common sailor may understand and practise it; and which, at the same time, from the trials I have made of it, seems to be as exact a method as any that has yet been thought of. Take a clean towel, or any other piece of cloth; ; dry dry it well before the sun or before the fire, then weigh it accurately, and note down its weight; dip it in the sea water, and, when taken out, wring it a little till it will not drip when hung up to dry; weigh it in this wet state, then dry it in the sun or at the fire, and when it is perfectly dry, weigh it again: the excess of the weight of the wetted cloth above its original weight, is the weight of the sea water imbibed by the cloth; and the excess of the weight of the cloth after being dried, above its original weight, is the specific gravity of the salt retained by the cloth; and by comparing this weight with the weight of the sea water imbibed by the cloth, we obtain the proportion of salt contained in that species of sea water."

Whoever undertakes to ascertain the quantity of salt contained in sea water, either by this or any other method, would do well to observe the state of the weather preceding the time when the sea water is taken out of the sea; for the quantity of salt contained in the water near the surface, may be influenced, both by the antecedent moisture, and the antecedent heat of the atmosphere. And this leads to the consideration of a question proposed by Aristotle, Why are the upper parts of the sea salter and warmer than the lower? Some philosophers, admitting the fact, have followed him in attempting to explain it; whilst others have thought themselves authorized by experiment to deny the truth of the position; and those, perhaps, will argue with the greatest justness, who shall affirm that it is neither generally to be admitted, nor generally to be rejected, but that the sea in some places, and under certain circumstances, is salter and warmer at the surface, than at any considerable depth beneath it, while in many others the reverse is true. The question consists of two parts, betwixt which, though there probably is a connection, yet it is not so necessary a one as to hinder us from considering each part by itself.

With regard to the use of this salt property of sea water, it is observed, that the saltness of the sea preserves its waters pure and sweet, which otherwise would corrupt, and emit a stench like a filthy lake, and consequently that none of the myriads of creatures which now live therein could exist. From thence also the sea water becomes much heavier, and therefore ships of greater size and burden are safely borne thereon. Salt water also does not freeze so soon as fresh water, hence the seas are more free for navigation