456 
NATURE 
[April 6, 1871 
ee 
tie application of cold at the surface is, in the case of sea-water, 
precisely equivalent as a moving force to the application of heat 
at the bottom, the motor power of which is universally admitted, 
—being practically utilised, in keeping up the circulation through 
the hot water warming apparatus now in general use.* The 
movement thus maintained would not, on the hypothesis, be a 
rapid one, but a gradual creeping flow ; since the absence of 
limit would prevent the power which sustains it from acting as 
an accelerating force, as it would do if the equatorial and polar 
areas were connected only by a narrow channel, like the Atlantic 
Ocean and the Mediterranean Sea. 
That the vertical circulation here advocated on a p-7or7 grounds, 
actually takes place in any mass of salt water of which one part 
is exposed to surface-cold and another to surface-heat, is capable 
of ready experimental proof :—Let a long narrow trough with 
glass sides be filled with salt water; and let heat be applied at 
one end (the equatorial) by means of a thick bar of metal laid 
along the surface, with a prolongation carried over the end of 
the trough into the flame of a spirit-lamp; whilst cold is 
applied at the other (the polar) by means of a freezing-mixture 
contained in a metallic box made to lie upon the surface, or 
(more simply) by means of a piece of ice wedged in between 
the sides of the trough. A circulation will immediately com- 
mence in the direction indicated by the theory; as may be 
readily shown by introducing some 4/ve colouring liquid at the 
polar surface, and some ved liquid at the equatorial surface. 
The blue liquid, as it is cooled, at once descends to the bottom, 
then travels slowly along until it reaches the equatorial end of 
the trough, then gradually rises towards the heated bar, and 
thence creeps along the surface back to the polar end. The red 
liquid first creeps along the surface towards the polar end; and 
then travels through exactly the same course as the blue had pre- 
viously done. + 
That such a vertical circulation really takes place in oceanic 
water, and that its influence in moderating the excessive cold of 
the polar areas and the excessive heat of the equatorial region is 
far more important than that of any surface-currents, seems to 
us a legitimate deduction from the facts stated in the Report of 
the “‘ Porcupine” Expedition for 1869. For, on the one hand, it 
was shown that there is a general diffusion of an almost glacial 
temperature on the bottom of the deep ocean-basins, at depths 
exceeding 1000 fathoms, occupied by polar water, more or 
less diluted by admixture according to the length of the course 
it has had to travei ; whilst between this stratum and that other 
stratum of warmer water which (on the hypothesis) is slowly 
moving pole-wards, there is a ‘‘stratum of intermixture,” in 
which there is such a rapid change of temperature as might be 
expected from the relation of the upper and lower masses of water. 
This “‘ stratum of intermixture” showed itself in a most marked 
manner in the Atlantic temperature-observations of the present 
expedition ; the descent of the thermometer, which had been 
very slow with increase of depth between 100 and 800 fathoms, 
becoming suddenly augmented in rate; so that between 800 
and 1000 fathoms it fell nine degrees, namely, from 49°°3 to 
fons’ 
‘ On the other hand, it was shown in the previous report 
that there is evidence of the slow pole-ward movement 
of a great upper stratum of oceanic water, carrying with 
it a warm temperature; which movement cannot be attri- 
buted to any such local influences as those which produce the 
Gulf-stream or any other currents put in motion by swz/ace- 
action. Of such a movement, it was contended, we have a 
marked example in that north-easterly flow which conveys the 
warmth of southern latitudes to the west of Ireland and Scotland, 
the Orkney, Shetland, and Faroe islands, Iceland, Spitzbergen, 
and the polar basin generally. This flow, of whose existence 
conclusive evidence is derived from observations of the tempera- 
ture of these regions, is commonly regarded as a prolongation of 
the Gulf-stream ; and this view is maintained not only by Dr. 
* The only scientific writer who has even approached what appears to us 
the truth on this point, is Captain Maury, whohas put forward the doctrine 
of a general interchange between the equator and the poles, resulting from 
a difference of specific gravity caused inter adza by difference of temperature, 
But. as Mr. Croll remarks, * although Captain Maury has expounded his 
views on the cause of ocean currents at great length in the various editions 
of his work, yet it is somewhat difficult to discover what they really are. 
This arises from the general confused and sometimes contradictory nature of 
his hydrodynamical conceptions.” See Mr, Croil’s Paper ‘‘ On the Physical 
Cause of Ocean Currents,” in the ‘‘ Philosophical Magazine” for October, 
1870. 
t This experiment has been exhibited, by the kindness of Prof, Odling, 
at the Royal Institution, and at the Royal Geographical Society. 


Petermann,* who has recently collected and digested these obser- 
vations with the greatest care, but also by Prof. Wyville Thom- 
son,t as well as by Mr. Croll.t Having elsewhere fully stated 
our objections to this doctrine, and discussed the validity of the 
arguments a lduced in support of it, § we shall here only record 
the conclusions which a careful examination of the present state 
of our knowledge of the subject has led us to form :— 
I. That there is no evidence, either from the surface-temperature 
of the sea, or from the temperatur: of sea-board stations along 
the western coast of Southern Europe, that the climate of that 
region is ameliorated by a flow of ocean-water having a tempera- 
ture higher than that of the latitude: the surface-temperature of 
the Mediterranean Sea, which is virtually excluded from all 
oceanic circulation, being higher than that of the eastern margin 
of the Atlantic in corresponding latitudes ;and the climate of 
sea-board stations on the Mediterranean being warmer than that 
of stations corresponding to them in latitude on the Atlantic coast 
—and this not merely in summer, but also in winter. This oceanic 
region may therefore be designated the eutrad area. 
II. That the evidence of climatic amelioration increases in pro- 
portion as we pass northwards from the wewtral area ; becoming 
very decided at the Orkney, Shetland, and Faroe islands. But 
that, as was shown by the /orcupine temperature-soundings 
of 1869, the flow of warm water which produces this ameliora- 
tion extends to a depth of at least 700 fathoms. 
III. That this deep stratum of water can be shown, by the cor- 
respondence in the rate of its diminution of temperature with 
depth, to be derived from the neutral area to the south-west ; 
where, as is shown by the Porcupine temperature-soundings 
of 1870, it is separated by a distinct ‘‘ stratum of intermixture” 
from the deeper stratum that carries polar waters towards the 
equator. 
IV. That the slow north-easterly movement of such a mass of 
water cannot, on any known hydrodynamical principles, be 
attributed to propulsive power derived from the Gulf-stream ; the 
last distinctly traced edge of which is reduced to a stratum cer- 
tainly sot exceeding 50 fathoms in depth, and not improbably less. 
V. That on the other hand, this slow pole-ward movement of 
the upper layer of the North Atlantic, down to the ‘‘stratum of 
intermixture,” is exactly what might be expected to take place as 
the complement of the flow of glacial water from the polar to the 
equatorial area ; the two movements constituting a general verti- 
cal oceanic circulation. 
VI. That there isa strong probability that the quantity of water 
discharged by the Gulf-stream has been greatly over-estimated, in 
consequence of the rate of the surface-current having been 
assumed as the rate of movement through the whole sectional 
area, which is contrary to all analogy; whilst there is also a 
strong probability that there is a reverse undercurrent of cold 
water through the narrows, derived from the polar current, that 
is distincly traceable nearly to its mouth. The upper stratum of 
this southerly current comes to the surface between the Gulf-stream 
and the coast ef the United States ; whilst its deeper and colder 
stratum underlies the Gulf-stream itself. || 
VII. That there is a strong probability that the quantity of 
heat carried off by the water of the Gulf-stream has been greatly 
over-estimated; the temperature-soundings taken during the cruise 
of the Porcupine in the Mediterranean having shown that the 
very high temperature of the surface extends but a little way 
down ; whilst the temperature observations in the Atlantic show 
that the descent into a cold stratum beneath may be very rapid. 
Hence the average of 65° assumed by Mr. Croll on the basis of 
observations made at considerable intervals of depth, is altogether 
unreliable. 
VIII. That the most recent and trustworthy observations in- 
dicate that the edge of the Gulf-stream to the north-east of the 
banks of Newfoundland is so thinned out and broken up by 
interdigitation with polar currents, that its existence as @ con- 
* Geographische Mittheilungen, 1870, p. 201. 
+ Lecture ‘On Deep-sea Climates,” in NaTuRE, July 28, 1870. 
a aematt “On the Physical Cause of Ocean Currents,” in ‘‘ Phil. Mag., 
ict. 1870. 
§ Proceedings of the Royal Geographical Society, for Jan. 9, 1871. 
|| That there isa slow southerly movement of Arciic water .beneath the 
Culf-stream, is indicated by the fact that icebergs have been seen moving 
southwards in direct opposition to its surface-flow ; their deeply-immersed 
portions presenting a larger surface to the lower stratum than their upper 
part does to the more superficial layer, as in the case of our “ current-drag.” 
And similar evidence is afforded by the southward drift of the buoy which 
was attached to the Atlantic Cable of 1865, but which broke away from it, 
apparently cartying with it a great length of the wire rope by which it had 
been attached. 
