252 

NATURE 

whole year, instantly declares itself as one of a system of curves 
which are referred to the Strait of Florida as the source of heat, 
and the warm water may be traced (and this is not begging the 
question, for the temperature is got by dipping the thermometer 
in the water), in a continuous stream, indicated where its move- 
ment can no longer be observed by its form, fanning out from the 
neighbourhnod of the Strait across the Atlantic, skirting the 
coasts of France, Britain, and Scandinavia, rounding the North 
Cape, and passing the White Sea and the Sea of Kari, bathing 
the western shores of Novaja Semlaand Spitzbergen, and finally 
coursing round the coast of Siberia, a trace of it still remaining 
to try to find its way through the narrow and shallow 
Behring’s Strait into the North Pacific. Now it seems to me 
that if we had these observations alone, which are merely de- 
tailed and careful corroborations of many previous ones, and could 
depend upon them, without even having any clue to their 
rationale, we should be forced to admit that whatever might 
be the amount and distribution of heat derived from a general 
eceanic circulation, whether produced by the prevailing winds of 
the region, by convection, by unequal barometric pressure, by 
tropical heat, or by arctic cold, there is besides this some other 
source of heat at the point referred to by these curves sufficiently 
powerful to mask all the rest, and, broadly speaking, to produce 
of itself all the perceptible deviations of the isotherms from their 
normal course. 
But we have no difficulty in accounting for this source of 
heat. As is well-known, about the equator, the north-east 
and south-east trade winds reduced to meridional directions 
by the eastward frictional impulse of the earth’s rotation, drive 
before them a magnificent surface current of hot water, the 
cquatorial current, 4,000 miles long and 450 miles broad, at an 
average rate of thirty miles a-day. This current splits upon 
Cape St. Roque, and one portion trends southwards to deflect 
the isotherms of 21° 15°5, 10, and 4°5° C. into loops, thus 
carrying a scrap of comfort towards the Falklands and Cape 
Hoorn. While the remainder, “ having made the circuit of the 
Gulf of Mexico, issues through the Straits of Florida, clinzing 
in shore round Cape Florida, whence it issues as the Gulf Stream, 
in a majestic current upwards of 30 miles broad, 2,200 feet 
deep, with an average velocity of 4 miles an hour, and a tempera- 
ture of 86° Fahr.” (Herschel.) 
I need scarcely follow the course of the Gulf Stream in detail, 
it is generally so well known, After leaving the Strait of Florida, 
it strikes ina north-easterly direction conformable generally to 
the easterly impulse given by its excess of diurnal rotation, to- 
wards the coast of Northern Europe. About 42° N. a large 
portion of it, still maintaining the high surface temperature of 
24° C., turns eastward and southward, and, eddying round the 
Sargasso Sea, fuses with the northern edge of the equatorial 
current, and rejoins the main circulation. The main body, how- 
ever, moves northwards. Mr, Croll, in a very suggestive paper 
in the LArlosophical Magazine on Ocean Currents, estimates the 
Gulf Stream as equal to a stream of water fifty miles broad and 
1,c00 feet deep, flowing at a rate of four miles an hour, with a 
mean temperature of 18°C. I see no reason whatever to believe 
this calculation to be excessive, and it gives a graphic idea of 
the forces at work. 
The North Atlantic and the Arctic Seas form together a basin 
closed to the northward, for there is practically no passage for a 
body of water through Behring’s Strait. Into the corner of this 
basin, as if it were a bath, with a north-easterly direction given 
to it, as if the supply pipe of the bath were turned so as to give 
tle hot water a definite impulse, this enormous flood is poured 
day and night, winter and summer; almost appalling in its 
volume and the continuity of its warmth, and its blueness, and 
brilliant transparency 77 s@cula seculorum | 
The hot water pours, not entirely from the Strait of Florida, 
but partly from the Strait and partly ina more diffused current 
outside the islands, with a decided, though slight, north-easterly 
impulse on account of its great initial velocity. The North 
Atlantic is with the Arctic Sea a cu/-de-sac. | When this basin 
is full—and not till then—overcoming its northern impulse, the 
water tends southwards in the southern eddy, so that there is a 
certain tendency for the hot water to accumulate in the northern 
basin. It is to this tendency, produced by the absence of a free 
outlet to the Arctic Sea, that 1 would be inclined to attribute the 
special excess of the warmth of the north-eastern shores of the 
North Atlantic. 
When ascertaining with the utmost care and with the most 
trustworthy instruments, by serial soundings, the temperature of 
the area surveyed by the Porcupine in 1869, we found at a depth 

of 2,435 fathoms in the Bay of Biscay, that down to 50 fathoms 
the temperature of the sea was greatly affected by direct solar — 
radiation ; from 100 to 900 fathoms the temperature gradually 
fell from 10° C. to 4° C., and from goo fathoms to 2,435 the fall 
of temperature was almost imperceptibly gradual from 4° to 
Boni, 
The comparatively high temperature from 100 fathoms to 900 
fathoms I am certainly inclined to attribute to the northern accu- 
mulation of the water of the Gulf Stream. The radiant heat de- 
rived directly from the sun must of course be regarded as a con- 
stant quantity superadded to the original temperature of the water 
derived from other sources. Taking this into account, the surface 
temperatures in what we were in the habit of calling the “ warm 
area’ coincided precisely with Petermann’s curves indicating the 
northward path of the Gulf Stream. 
It is scarcely necessary to say that for every unit of water which 
enters the basin of the North Atlantic, an equivalent must return. 
From its low velocity, the Arctic return current or indraught will 
doubtless tend slightly to a westerly direction, and the higher 
specific gravity of the cold water may probably even more power- 
fully lead it into the deepest channels ; or possibly the two causes 
may combine, and in the course of ages the currents may tend to 
hollow out deep south-westerly grooves. At all events, the main 
Arctic return currents are very visible on the chart taking that 
direction, indicated by marked deflections of the isothermal lines. 
The most marked is the Labrador current, which passes down 
inside the Gulf Stream along the coasts of Carolina and New 
Jersey, meeting it in the strange, abrupt “cold wall,” dipping 
under it as it issues from the Gulf, coming to the surface again*on 
the other s'de, and a portion of it actually passing under the Gult 
Stream as a cold counter-current into the deeper part of the Gulf 
of Mexico. 
Fifty or sixty miles out from the west coast of Scotland, I 
believe the Gulf Stream forms another through a very mitigated 
““cold wall.” In 1868 Dr. Carpenter and I investigated 
a very remarkable cold indraught into the channel between 
Shetland and Faroe. Ina lecture on deep-sea climates, which 
was published in NaTuRE, in July last, I stated my belief that 
the current was entirely banked up in the Faroe channel by the 
Gulf Stream passing its gorge. 
Since that time I have been led to suspect that a part of the 
Arctic water oozes down the Scottish coast much mixed, and 
sufficiently shallow to be affected throughout by solar radiation. 
About sixty or seventy miles from shore the isothermal lines have 
a slight but uniform deflection, Within that line types charac- 
teristic of the Scandinavian fauna are numerous, and in the course 
of many years’ use of the towing net, I have never met with any 
of the Gulf Stream pteropods, or of the lovely Polycystinze 
and Acanthometrinz, which absolutely swarm beyond that limit. 
The differences in mean temperature between the east and w st 
coasts of Scotland, amounting to between 1° and 2° Fahr., ‘s 
also somewhat less than might have been expected. 
There is another point which is worthy of consideration. It 
is often said that about the latitude 45° N. the Gulf Stream thins 
out and disappears. The course of a warm current is traced far- 
ther on the maps, even to the coast of Norway and the North 
Cape, but this north-easterly extension is called the Gulf Stream 
drift, and is supposed to be a surface flow caused by the pre- 
vailing S.W. anti-trades. There seem to me to be several 
arguments against this view. The surface of the sea, at all events 
between 40° and 55° N., has a mean temperature higher than 
that of the air, and that could scarcely be the case unless there 
were a constant supply, independent of the wind, of water from 
a warmer source ; and any question is, to my mind, entirely set 
at rest by our establishment of the mass of warm water moving 
to the north-eastward, whose curves of excess of temperature, 
so far as they have as yet been ascertained, correspond entirely 
with those of the Gulf Stream. 
I cannot at present enter at any length into the very funda- 
mental question which has lately given rise to so much discussion, 
whether the Gulf Stream is actually the agent in conveying 
heat to the North Atlantic and ameliorating the climate 
of its north-eastern shores, or whether these results are not 
rather produced by a *‘ general oceanic circulation.” 
As, however, I am frequently quoted by my friend and col- 
league in much scientific work, Dr. Carpenter, as holding an 
opinion different from his, and as my present remarks place my 
views beyond doubt, it may be well to give a reason for my want 
of faith, Dr. Carpenter’s view, if I understand him rightly, is 
that there isa great general convective circulation in the ocean, on 
the principle of a hot-water heating apparatus, and that the Gulf 


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