Of the various phenomena of the sea, that of its _saltness_ is one of
the most obvious. No questions concerning the natural history of our
globe have been discussed with more attention, or decided with less
satisfaction, than that concerning its primary cause, which had
perplexed the philosophers before the time of Aristotle, and surpassed
even the great genius of that profound inquirer into natural causes.
Kircher, after having consulted not less than thirty-three authors on
this 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.
This question does not seem capable of admitting an illustration from
experiment; at least, not from any experiments hitherto made for that
purpose: it is, therefore, not surprising, that it remains nearly as
problematical in the present age, as it has been in any of the
preceding. Had observations been made three or four centuries ago, to
ascertain the saltness of the sea, then, at any particular time and
place, we might now, by making similar observations at the same place,
in the same season, have been able to know, whether the saltness, at
that particular place, was increasing or decreasing, or an invariable
quantity. This kind and degree of knowledge would have served as a clue
to direct us to a full investigation of this matter in general. It is to
be regretted, however, that observations of this nature have not, in
former days, been made with any degree of precision.
One of the principal opinions maintained on this subject by modern
philosophers, and more particularly supported by Halley, is, that since
river-water, in almost every part of the globe, is impregnated in a
greater or less degree by sea-salt, the sea must have gradually acquired
its present quantity of salt from the long continued influx of rivers.
The water which is carried into the sea by these rivers, is again
separated from it by evaporation, and being dispersed over the
atmosphere by winds, soon descends in rain or vapor upon the surface of
the earth, whence it hastens to pour into the bosom of the ocean the
fresh tribute of salt it has collected in its inland progress. Thus the
salt conveyed into the sea not being a volatile substance, nor
performing an incessant circulation, must be a perpetually increasing
quantity; and sufficient time, it is contended, has elapsed since the
creation, for the sea to acquire, from this source, its present quantity
of salt.
This opinion has been successfully combated; and it is denied that
freshwater rivers could, in the course of thousands or even millions of
years, have produced saltness in the sea. If this were the case, every
sea, or great body of water, which receives rivers, must have been salt,
and have possessed a degree of saltness in proportion to the quantity of
water which these rivers discharge. But so far is this from being true,
that the Palus Mæotis, and our great American lakes, do not contain salt
water, but fresh. It may indeed be objected, that the quantity of salt
which rivers carry along with them, and deposit in the sea, must depend
on the nature of the soil through which they flow, which may in some
places not contain any salt; and that this is the reason why the great
lakes in America and the Palus Mæotis are fresh. But to this opinion,
which is merely hypothetical, there are insurmountable objections. It is
a curious fact, that the saltness of the sea is greatest under the
equator, and diminishes gradually toward the poles; but it can not
therefore be assumed that the earth contains more salt in the tropical
regions than in the temperate zones, and more in these again than in the
frigid zones. On the other hand, if it be allowed that the sea receives
its saltness from the rivers, it must be equally salt, or nearly so, in
every part of the earth; since, according to a simple and well-known
principle in chemistry, _when any substance is dissolved in water with
the assistance of agitation, at whatever part of the water it is
introduced, it will be equally diffused through the whole liquid_. Now,
though it were true that a greater quantity of salt should have been
introduced into the sea under the equator, than toward the poles, from
the constant agitation occasioned by the wind and tide, the salt must
have soon pervaded the whole mass of water. Neither is this greater
proportion of saltness owing to a superior degree of heat, since it is
an established principle in chemistry, that cold water and hot water
dissolve nearly the same proportion of salt.
The saltness of the sea has also been ascribed to the solution of
subterraneous mines of salt, that are supposed to abound in the bottom
of the sea, and along its shores. But this hypothesis can not be
supported. If the sea were constantly dissolving salt, it would soon
become saturated; for it can not be said that it is deprived of any
portion of its salt by evaporation, since rain-water is fresh. If the
sea were to become saturated, neither fishes nor vegetables could live
in it. It may hence be inferred that the saltness of the sea can not be
accounted for by secondary causes, and _that it has been salt since the
beginning of time_. It is indeed impossible to suppose that the waters
of the sea were at any time fresh since the formation of fishes and
sea-plants; neither will they live in water which is fresh. It may hence
be concluded that the saltness of the sea has, with some few exceptions,
perhaps arising from mines of rock-salt dispersed near its shores, been
nearly the same in all ages. This hypothesis, which is the simplest, and
is involved in the fewest difficulties, best explains the various
phenomena dependent on the saltness of the sea.
Although this saline property may be one of the causes by which the
waters of the sea are preserved from putridity, still it can not be
considered as the principal cause. The ocean has, like rivers, its
currents, by which its contents are circulated round the globe; and
these may be said to be the great agents which keep it sweet and
wholesome. A very enlightened navigator, Sir John Hawkins, speaks of a
calm, in which the sea, having continued for some time without motion,
assumed a very formidable aspect. “Were it not,” he observes, “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 the Azores, almost six months,
the greater part of which time we were becalmed. Upon which, all the sea
became so replenished with various sorts of gellies, 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, toward 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 diseased, and a preservative to those who were not
touched.”