the depth of the sea is in genera! 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 ana- 
logy holds at a distance from the shore, ex- 
periments alone can determine. 
To calculate the quantity of water con- 
tained in the sea, while its depth is unknown, 
is impossible. But if we suppose with Buf- 
fon that its medium depth is the fourth part 
of a mile, the ocean, if its superficies is 
128,235,759 square miles, will contain 
32,058,939,75 cubic miles of water. 
Let us now endeavour to compute the 
quantity of water which is constantly dis- 
charged into the sea. For this purpose let 
us take a river whose velocity and quantity 
of water are known, the Po, for instance, 
which, according to Riccioli, is 1000 feet (or 
100 perches of Boulogne) broad, ten feel- 
deep, and runs at the rate of four miles in an 
hour ; consequently that river discharges 
into the sea 200,000 cubic perches of water 
in an hour, or 4,800,000 in a day. A cubic 
mile contains 125,000,000 cubic perches; 
the Po therefore will take twenty-six days to 
discharge a cubic mile of water into the sea. 
Let us now suppose, what is perhaps not very 
far from the truth, that the quantity of wa- 
ter which the sea receives from the rivers in 
any country is proportioned to the extent of 
that country. The Po from its origin to its 
mouth traverses a country 380 miles long, 
and the rivers which fall into it on every side 
rise from sources about sixty miles distant 
from it. The Po, therefore, and the rivers 
which it receives, water a country of 45,000 
square miles. Now since the whole super- 
ficies of the dry land is about 42,745,253 
square miles, it follows, from our supposition, 
that the quantity of water discharged by all 
the rivers in the world, in one day, is thirty- 
six cubic miles. If, therefore, the sea con- 
tains 32,058,939 cubic miles of water, it 
would take all the rivers in the world 2439 
years to discharge an equal quantity. 
It may seem surprising that the sea, since 
it is continually receiving such an immense 
supply of water, does not visibly increase, 
and at last cover the whole earth. But our 
surprise will cease, if we consider that the 
rivers themselves are supplied from the sea, 
and that they do nothing more than carry 
back those waters which the ocean is conti- 
nually lavishing upon the earth. Dr. Halley 
has demonstrated that the vapours raised 
from the sea and transported upon land are 
sufficient to maintain all the rivers in the 
world. The simplicity of this great process 
is astonishing : the sea not only connects dis- 
tant countries, and renders it easy to trans- 
port the commodities of one nation to ano- 
ther, but its waters rising in the air descend 
in showers to fertilise the earth and nourish 
the vegetable kingdom, and collecting into 
livers flow onwards, bringing fertility and 
wealth and commerce along with them, and 
again return to the sea to repeat the same 
round. 
As the sea covers so great a portion of the 
globe, we should no doubt, by exploring its 
bottom, discover a vast number of interest- 
ing particulars. Unfortunately, in the great- 
Vol. II. 
er part of the ocean this lfos hitherto been 
impossible. Part, however, has been exa- 
mined ; and the discoveries which this exa- 
mination has produced may enable us to 
form some idea at least of the whole. The 
bottom of the sea, as might have been con- 
jectured indeed beforehand, bears a great 
resemblance to the surface of the dry land, 
being, like it, full of plains, rocks, caverns, 
and mountains ; some of which are abrupt 
and almost perpendicular, while others rise 
with a gentle declivity, and sometimes town- 
above the water and form islands. Neither 
do t he materials differ which compose the 
bottom of the sea and the basis of the dry 
land. If we dig to a considerable depth in 
anv part of the earth, we uniformly meet 
with rock ; the same thing holds in the seal 
The strata too are of the same kind, disposed 
in the same manner, and form indeed but one 
whole. The same kind of mineral and bitu- 
minous substances are also found interspersed 
with these strata ; and it is to them probably 
that the sea is indebted for its bitter taste. 
Over these natural and original strata an ar- 
tificial bed has pretty generally been formed, 
composed of different materials in different 
places. It consists frequently of muddy tar- 
tareous substances firmly cemented together, 
sometimes of shells or coral reduced to pow- 
der, and near the mouths of rivers it is gene- 
rally composed of fine sand or gravel. 
4 he ocean differs more in saltness in different 
climates towards the equator than nearer the 
poles. This seems to arise from the different 
quantities of water which -are evaporated, in 
proportion to those which fall in rain. One 
pound of sea-water in the Baltic yields about 
a quarter of an ounce of salt ; near Holland 
half an ounce; and in the British seas about 
two ounces. Boyle has also observed, that in 
places of great depth the water is saltest at 
the bottom. 
In the voyage made towards the north 
pole in 1773, it was found that the sea-water 
at the Nore contained not quite one thirty- 
sixth of salt; at the back of Yarmouth sands, 
not quite one thirty-second ; off Flamborough 
Head, rather more than one twenty-ninth ; 
off Scotland, rather less than one 'twenty- 
ninth ; latitude 74°, at sea, one twenty-ninth ; 
and in latitude 78°, rather le9s than one 
twenty-eighth. 
The cause of the saltness of the ocean has 
been a subject of investigation among phi- 
losophers in almost all ages, but it still remains 
in great obscurity, There can be little 
doubt that a large quantity of saline mat- 
ter existed in this globe' from the crea- 
tion ; and, at this day, we find immense beds 
of sal gem, or common salt, buried in the 
earth, particularly at Cracow ; but whether 
these collections have been derived from the 
ocean, and deposited in consequence of the 
evaporation of its waters in certain circum- 
stances ; or whether the ocean was itself ori- 
ginally fresh, and received its salt from col- 
lections of saline matter situated at its 
bottom, or from that brought by the in- 
flux of rivers ; cannot now be ascertain- 
ed, No accurate observations on the degree 
of saltness of the ocean in particular latitudes 
were made till the present century, and it 
is not possible, therefore, to ascertain what 
was the state of the sea at any consider- 
able distance of time, nor, consequently, 
whether its degree of saltness increases, de~ 
6‘4 L 
creates, or is stationary. From differences 
among aquatic animals, however, some of 
which seem adapted to salt water, and some 
to fresh, it is probable, that both these states 
of water existed from the creation of the 
world. We know, it is true, that some kinds 
of fish, as salmon, are capable of existing 
both in fresh and in salt water, and that habit 
has a powerful influence overall animals ; but 
this is not sufficient to refute the main fact, 
that some kinds of risk thrive only in salt wtf- 
ter, others in fresh; some in standing' pools,- 
and others in rapid currents. 
That excellent philosopher and chemist* 
the bishop of Lendaff, has recommended a 
most simple and easy mode of ascertaining' 
the saltness of the sea in any latitude ; and 
as the language, in point of perspicuity and 
correctness, cannot be improved, we take the 
liberty of inserting it in his own words : 
“ As it is not every person who can make 
himself expert in the use of the common 
means of estimating the quantity of salt con- 
tained in sea-water, I will mention a method 
of doing it which is so easy and simple, that 
every common sailor may understand and prac- 
tise it, and which, from the trials 1 have made 
of it, seems to be as exact a method as any 
that has yet been thought or. Take a clean 
towel or any other piece of cloth, dry it well 
in 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 
either 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 ori- 
ginal 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 weight 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 propor- 
tion of salt contained in that species of seq- 
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 an- 
tecedent beat of the atmosphere.” 
Whether the sea is sailer or not at different 
depths, notwithstanding Mr. Boile’s obser- 
vations before quoted, has not yet been pro- 
perly ascertained ; but that its temperature 
varies considerably in proportion to the 
depth we have decisive proof. 
“ With respect to the temperature,” savs 
bishop Watson, “ of the sea at different 
depths, it seems reasonable enough to sun- 
pose, that in summer time it will be hotter 
at the surface than at any considerable depth 
below it, and that in winter it will be colder. 
“ Mr. Wales describes the instrument he 
made use of for trying the temperature of 
the sea at different depths, in the following 
terms : ‘ The apparatus for trying the sea- 
water at different depths consisted of a square 
wooden tube of about eighteen inches ionn 
and three inches square externally. It was 
fitted with a valve at the bottom, and another 
at the top, and had a contrivance for sus* 
