The herald and mail. [volume] (Columbia, Tenn.) 1873-188?, 1875-10-22
OCEAN CIRCULATION

fills Its OCean-bsSin. This influence, sup
posing that water to be otherwise station
AIRY, will be simply nil; for the water ly-
ing ndereach parallel will have the same
rate of rotation from west to east, as the
solid earth in that parallel. But suppose
that a 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 a we'll
known principle of physics, carry with it
the easteTly momentum of the parallel it
has quoted, into a parallel which has a
different rate of eastward movement; and
thus, if flowing from a 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,
iftiOwing from higher to a lower latitude,
1t Will arrive at the latter with a deficiency
of easterly momentum, causing it to be
Gas 1t were) left behind, so as to tend con-
stantly towards the west. Now. the ex-
cess of easterly momentum possessed by
the gulf stream, in virtue of its nOrtherlv
flow, was rightly assigned by Captain
Maury, and accepted by Sir John Her
schel, As a principal cause of its eastward
change of direction where the parallels of
ATTITUDES are rapidly shortening; and ap-
ply the same principle to explain the very
strong eastward tendency of the poleward
uppcr-flow, which carries it not only to the
shores of Norway, but past the North
CapCs towards Nova Zcmbla 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 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-fiow has a constant movement,
however slow, towards the Equator, it
must carry with 1t adeficiency Of easterly
momentum, which will cause it to creep
up the slope that forms the western Dor
der of the Atlantic basin; and thus the
upward slant of the deep, cold strata in
this situation becOmesan evidentiary fact
of singular COgency, in favor of the actual
existence of that southwark movement
which has been shown to be probable on
uPriOTj grOunds-no other way of ac-
counting for that slant being discernible.
1t Is fact of no little interest, that, as
/ learn from DIR. Meyer of Kiel, who has
made a special study of the temperature
of the North Sea, a similar popularity
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 a 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 DIR. Meyer has found a sudden re-
ductlOn 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.. J. Gwyn Jeffreys-viz
the presence of arctic mollusks on the
DOggef 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
lantic seabOard of the southern states) to
4 surface-current from the north, of which
IN neither case Is there any evidence.
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
ptrature-seCtiOn are the great thickness
OF the upper stratum above the isotherm
of 4Oo, which lies at a depth of about
nine hundred fathOms between the Azores
and Madeira; and the special thickness,
in the western half of this section, of the
stratum between co. and go 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 courseO of the "Chal-
lenger' was turned Southwards, in a di-
rection ofgeneral Parallelism to the west
ern coast of Africa, until she approached
the equator; and we now encounter
remarkable change in the thermal strait
fication. For, whilst the suriace-temper-
allure progressively rose from 10 to 790,
this augmentation affected the superficial
stratum alone; the isotherm of go re-
manned parallel to the surface; but all
the subiacent isOtherms were found to
slant upwards. that of 4O' rising from
nine hundred and fifty fathOms halfway
between Madeira and 1t. Vincent to six
hundred and fifty fathoms off st. Vim
cent, and to four hundred and fifty faith
Dms in g y. lat.,-thus confirming in
most remarkable manner the conclusion
of Lcnl that the polar under-iow rises
towards the surface in the equatorial
zone.
The challenger" then crossed the
Atlantic for the third time between 90 \.
lat. and Il :. lat, passing st. PauGs Rock
and Fernando NOronha, and thence pro-
Cecding to PeTnamhuco, lat 10 :. The
facts brought to light in this part of her
survey may be considered as surpassingin
interestall that had been previously asCer-
tanned; their confirmation of the doctrine
she was directed to test being of crucial
value, For in the temperatUTe-section
here obtained, these two features are spe-
Cially nOtiCeabe-tirst, the further reduc-
ton of bottom-temperaturc, and, second,
the yet nearer approach of the lsotherm
of 40 to the surface. Almost precisely
uuder the Line, 4 bottom temperature of
32'4' was obtained at a depth of 2,475
fathOms; and as the isotherm of 30 (thc
lowest temperature that the arctic I'M
dertiow could here bear) lay at the depth
of about eighteen hundred fathoms, it Is
obvious that the stratum of 615 fathOms
must entirely consist of water that has
found its wav thither from the antarctic
area. But this Is OVERLAND by stratum
of fifteen hundred fathomS' thickness, |
whose temperature ranges between 80
and 4O'; thus actually carrying IN the
isothcrm of 40 to within three hundred
fathoms of the surface. From 7So at the
surface, the thermometer was found to
fall to SO within one hundred fathomS |
Just "a it does in the Mediterranean but |
whilst in that inland sea the temporal !
turc remains constant from that point to |
the bottom, it goes on falling, beneath |
the equatorial sun, to 49, at about two |
hundred and twenty fathoms, to 4O' at |
less than three hundred, and thence pro- |
excessively to the bottom-temperature Of |
32'4' through a stratum Of more than |
two thousand fathoms' thickness. Now. /
rs the lowest surface-temperature of the |
whole year cannot be here less than 80. |
II is clear that the influence of what NAV
be called imported cold ranges from |
4ha bnttnro yFbara II l. most