The Canton mail. [volume] (Canton, Miss.) 18??-1882, 1875-10-23
ooEAN CIRCULATION.


viz, the influence of the earth's rotation
upon the movement of the water which
fins its ocean-basin. This influence, sup
v,os;no; that water to be otherwise station
arv will be simply nil; for the water ly-
mo under each parallel will have the same
rate of rotation front west to east, as the
solid earth in that parallel. But suppose
that large body of water has a move
ment of its own, either from a lower to a
higher, or from higher to a lower par
allel; it will then, according to we'll
known principle of physics, carry with it
the easterly momentum of the parallel 1t
has quieted, into parallel which has a
different rate of eastward movement; and
thus, if flowing from lower to a higher
latitude, it will carry with it an excess of
easterly momentum which will cause it to
tend constantly towards the east; whilst,
ifflowing from higher to lower latitude,
it will arrive at the latter with deficiency
of easterly momentum, causing it to be
(as it were) left behind, so as to tend con-
stantly towards the west. Now, the ex-
csss of easterly momentum possessed by
the gulf stream, in virtue of its northerly
flow, was rightly assigned by Captain
Maury, and accepted by Sir John Her
schel, as principal cause of its eastward
change of direction where the parallels of
ATTITUDES are rapidly shortening; and ap-
ply the same principle toexplain the very
strong eastward tendency of the poleward
upper-fow, which carries it not only to the
shores of Norway, but past the North
Capes towards Nova Zembla. But if this
be true, the converse also will be true in
regard to any southwark movement of
arctic water; and thus we see not only
why the continuation of the Greenland
and Labrador current should have a west
erly tendency which keeps it close to the
shore of the United States, but also why
the glacial under-fow should approach
the surface along the coast-line. For if
this under-how has a constant movement,
however slow, towards the Equator, it
must carry with it deficiency of easterly
momentum, which will cause it to creep
up the slope that forms the western ber-
der of the Atlantic basin; and thus the
upward slant of the deep, cold strata in
this situation becomes an evidentiary fact
of singular cogency, in favor of the actual
existence of that southwark movement
which has been shown to be probable on
a priori grounds-no other way of ac-
counting for that slant being discernible.
1t is fact of no little interest, that, as
I learn from DIR. Meyer of Kiel, who has
made special study of the temperature
of the North Sea, a similar popularity
presents itself near our own shores. The
greater part of that sea is so shallow, that
an elevation of no more than three hun
dred feet would convert it into dry land,
uniting the eastern coast of Great Brit
ain to continental Europe. But outside
the coast of Norway there is a much
deeper channel, along which there flows
southwards cold stream which can be
traced as far as the Skager rock; and this,
under the influence of its deficiency of
easterly momentum, flows up the western
slope of that channel, and spreads itself
over the floor of the North Sea as far as
the Dogger Bank, on the eastern slope of
which Dr. Meyer has found sudden re-
duction of no less than fifteen degrees of
temperature, in a vertical descent of no
more than five fathoms This extension
of the Norwegian cold under-stratum
affords the rationale of the remark |
able fact previously ascertained by the
dredgings of Mr.. ]. Gwyn Jefreys-viz Z,
the presence of arctic mollusks on the |
Dogger Bank; and it further explains |
the low sea-temperature of our eastern |
coasts, which had been previously attrib- |
uted (like the "cold bank" along the At |
1antic seaboard of the southern states) to |
surface-current from the north, of which |
~AA AOAbhSA SASC 10 thCiC any ONidShSC.
Returning now to the challenger"
we trace her course back from Halifax to |
Bermuda, and thence again across the |
Atlantic to the Azores and Madeira. The |
principal features of interest in this tenn
perature-section are the great thickness
Of the upper stratum above the isotherm |
of 400, which lies at depth of about |
nine hundred fathonns between the Azores |
and Madeira; and the special thickness, |
in the western half of this section, of the |
stratum between CO. and 650 Fair. We
shall be better prepared to understand
the meaning of these peculiarities, when |
we compare the thermal qualification of
the north with that of the south Atlantic.
From Madeira, the course of the 'sChal- !
lenger" was turned southwards, in di- |
rection ofgeneral parallelism to the west
ern coast of Africa, until she approached
the equator; and we now encounter a
remarkable change in the thermal strait |
fcation. For, whilst the surface-temper-
allure progressively rose from 10 to 790,
this augmentation affected the superficial
stratum alone; the isotherm of co. re-
manned parallel to the surface; but all
the subjacent isotherms were found to
slant upwards, that of 40o rising from
nine hundred and fifty fathoms halfway
between Madeira and st. Vincent to six
hundred and fifty fathoms off st. Vim
cent, and to four hundred and fifty faith
oms in 90 n. lat.,-thus confirming in a
most remarkable manner the conclusion
of Lenl- that the polar under-fow rises
towards the surface; in the equatorial
zone.
The challenger" then crossed the
Atlantic for the third time between 90 n.
lat. and 4o S. lat, passing st. PauPs Rock
and Fernando NorOnha, and thence pro-
ceeding to Pernambuco, lat 7'5' S. The
facts brought to light in this part of her
survey may be considered as SURPRISING in
interest all that had been previously ascer-
tanned; their confirmation of the doctrine
Hhe was directed to test being of crucial
value, For in the temperature-section
here obtained, these two features are spe-
cially noticeable-frst, the further reduc-
ton of bottom-temperature, and, second,
the yet nearer approach of the isotherm
of 4O' to the surface. Almost precisely
under the Line, a bottom temperature of
S2-4' was obtained at depth of 2,475
3athoms; and as the isotherm of $50 (the
lowest temperature that the arctic I'M
derfow could here bear) lay at the depth
of about eighteen hundred fathoms. it is
obvious that the stratum of 675 fathoms
1850 feet) in thickness beneath this,
must entirely consist of water that has
found its way thither from the antarctic
area. But this is overlaid by stratum
of fifteen hundred fathoms' thickness,
whose temperature ranges between $50
and 4O'; thus actually carrying No the
isotherm of 40' to within three hundred
fathoms,of the surface. From 78e at the
surface, the thermometer was found to-
fall to So within one hundred Hathoms Il
just as it does in the Mediterranean but,P
whilst in that inland sea the tenn er4.
ture remains CONSTANT from that point. to
the bottom, il bes on falling, beneath
the equatorial sun, to 49, at about two
hundred and twenty fathoms, to 40' at
less than three hundred, and thence pro-
gressively to the bottom-temperature of
32-4' through a stratum of more than
two thousand fathoms' thickness. Now,
az the lowest surface-temperature of the