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

limited current which has completely
died out by superficial expansion. Blu
if we admit that. alike in the North ano
in the South Atlantic, this upper stratum
is being drawn pole-wards by a ris
frontre generated by the continual de
scent of the water that comes under thu
influence of polar cold, we see how thu
excess of thickness it possesses in thu
northern hemisphere enables it to impair
to the atmosphere above it Il correspond
ing amount of warmth. For, as ever,
surtice-tilm that has given up its heat t
the air above ii, sinking until it meet
with water rs cold as itself, is replaced
by the uprising eff warmer water from
beneath, so. the further down the excess
of warmth extends, the longer will it b,
before the temperature of the surface Il
reduced to that of the air above-lust a
the surface of deep lake remains un
concealed bv II frost which forms a thick
LAYER of ice on shallow pond or mere.
1t was urged, several years ago, by the
f'1ate Mr. Findley. that surprising the Gull
Stream proper to have Il continuous on
ward movement to the western shores %
Great Britain, the thinness of its expan
sion, and the slowness of its rate, where
it is last recognizable us q current, would
subject it to the loss of all its surplu.
heat, long before it reaches our coast anG
this argument is strongly confirmed by
the fact, that the upper stratum of the
Mediterranean, though heated by the
summer sun to quite as high tempera
ture as that of the Gulf Stream in the
mid-Atlantic, loses its excess of warmth
with the seasonal reduction in the tenn
perature of the atmosphere above it;
| whilst, as soon as its surface has been
| Il. ,..trt
of the deep subjacent bed, it resists any
further reduction, whatever may be the
temporary depression of the atmospheric
temperature And in this manner we
find that the moderate, but permanent,
/ elevation of the uniformly heated mass
| of Mediterranean water, has 4 far more
potent influence in ameliOrating the eli
mate of its northern shores, than the
transient experimenting of its surface
layer.
But it does not hence follow that Mr..
Findley was right in attributing the
amelioration of the climate of north
western Europe, as DIR. Hayes has since
| done, solely to the heat transported by
the south-westerly winds; for the very
careful and systematic observations which
have now been carried on for some years
under the able direction of Professor
| Mohn, of Christiania, upon the relative
| temperatures of the air and the sea along
the coast of Norway, have shown that
the latter has an average excess of warmth
during the four winter months, amount
ing to 14'5o Fair. This excess he very
naturally attributed, in the first instance,
to the influence of the Gulf Stream; but
| he has latterly expressed his concurrence
| in my own view. that the poleward trans
INanf
a FAR larger and deeper movement, for
which the general oceanic circulation
alone can adequately account.
This view derives further confirmation
from the extension of the Challenger"
inquiries into the Antarctic Ocean, by a
southwark DETECTION from her course be-
tween the Cape of Good Hope and
Sydney. For it becomes plain, from an
examination of the temperature-sections
taken in this part of her voyage, that the
comparative coldness of the southern
oceans is essentially due, not so much to
the want of a superheated surface-layer,
as to the rapid reduction in the tempera-
ture of the whole comparatively thin
upper warm stratum under the influence
of atmospheric cold: the isotherm of
400, which lies below four hundred faith
oms in lat. 370 s., rising to one hundred
and fifty fathoms in lat. 46o s., and
actually coming to the surface near
Kerguelen's Land Cat. 500 s. while it
lies below eight hundred tathoms in the
corresponding northern parallel. Thusit
comes to pass that the summer climate of
Kerguelen's Land, as Captain Mares re-
marks, is comparable to the winter eli
mate of che British Isles; and that
glaciers there descend from the noun
tains almost to the waters edge, remind
ing us of the ice-sheet which covered the
surface of North Britain during the
glacial epoch.
The Challenger" approached the
antarctic ice-barrier in the height of the
southern summer, when the influence of
solar radiation was exerted in melting the
ice-bergs and the edge of the field-ice,
and thus in lowering rather than raising
the temperature of the surface-water
which was found to be pretty constantly
that of melting ice as far down as the
thickness of the ice extended. This was
exactly what had been anticipated; for
the water thus chilled does not descend,
but remains floating ut the surface, in
consequence of the lower proportion of
salt which it contains; and yet it does not
rise in temperature, because any further
accession of heat it may receive from the
sun is expended in melting more ice.
But underneath this stratum of half-salt
glacial water, there was found a stratum
of ordinary sea-water having a tempera-
ture between 32' and 80; and this was
obviously continuous with the proper
surface-stratum at such a distance from
the ice-barrier as to be out of the reach
of melting ice; whilst there was every
reason to believe that the whole subja-
Il to hot LII
perature of 80 or less. Now, it is
obvious that as this warmer stratum
could not have derived its heat from local
solar radiation, it must have brought ii
from elsewhere; and as there is no Gulf
Stream in the southern ocean, there
seems no other agency to account for its
presence, than the polar indraught which
has been so frequently referred to.
HThus the observations upon ocean tenn
perature hitherto collected by the Chal-
lenger," in the North, Equatorial, and
South Atlantic, in the Antarctic, and in
Eastern Archipelago, not only prove con-
formable in very particular to the doc
trine they were designed to test, but do
not seem capable of any other expla-
nation.
The OBSERVATION-DISCLOSURES recently
made in the North Pacific by the United
States ship "Tuscarora, which was
commissioned to carry a line of soundings
for telegraph cable this vast ocean-basin
from the coast of California to Japan,
making the Sandwich Islands halfway
us to test this doctrine
by a case which presents a marked dis
similarity of conditions. For, although
the North Pacific has communication
with the arctic basin through Behring's |
Strait, yet this is two shallow, as well as |
narrow, to admit of any outflow of |
glacial water from the latter into the |
former. Now, as the average depth of |
the North Pacific is considerably greater |
than that of the North Atlantic, and as
thefe is reason to believe that this excess
e4.tnds to the South Pacific ALSO we
should expect, on the principle already
stated Up. y, that the influence of an
tarctic cold will be strongly exerted
tb ron Ul,nut tbn yybnIa of ~. md tI,;. |