> 
_ of 800 to goo fathoms. 
the Gulf Stream which is deflected southwards; and 
places that portion of the Gulf Stream which makes its 
_perature of the surface of the earth is calculated at about 
Fuly 28, 1879] 
NATURE 
261 
passing through the Strait of Florida, and the whole 
generally called the Gulf Stream, of varying depth, but 
attaining off the west coast of Ireland and Spain a depth 
Secondly, of a general indraught | 
of Antarctic water compensating at all events that part of | 
thirdly, of a comparatively small quantity of Arctic water 
which, flowing through two or three narrow channels, re- 
way into the Arctic Sea. As I have already said, the 
Gulf Stream loses an enormous amount of heat in its 
northern tour. At, say a point 200 miles west of Ushant, 
where the observations at the greatest depth were made 
on board the Porcupine, a section of the water of the | 
Atlantic shows three surfaces, at which interchange of 
temperature is taking place. 1. The surface of the sea, 
that is to say, upper surface of the Gulf Stream layer, is 
losing heat rapidly, @ by radiation, 4 by contact with a 
layer of air, which is in constant motion, and perpetually 
being cooled by convection ; and ¢ by the conversion of 
water into vapour. As the cooling of the Gulf Stream 
layer takes place principally at the surface, the tempera- 
ture of the mass is kept pretty uniform by convection. 
2. The band of contact of the lower surface of the Gulf 
Stream water with the upper surface of the water of the 
cold indraught. Here the interchange of temperature 
must be very slow, though that it does take place is shown 
by the slight depression of the surface isotherms over the 
principal paths of the indraught. The cold water being 
below, convection in the ordinary sense cannot occur, and 
interchange of temperature must depend upon conduc- 
tion and diffusion, causes which in the case of masses 
of water of such depth must be almost secular in 
their action, and probably to a much greater extent 
upon mixture produced by local currents and by the 
tides. 3. The third surface is that of contact between 
the cold indraught and the bottom of the sea. The tem- 
11°C., but it would be completely cooled down by-anything 
like a movement and constant renewal of cold water ; all 
we can say, therefore, is that contact with the bottom 
can never be a source of depression of temperature. As 
a general result, the Gulf Stream water is nearly uniform 
in temperature throughout the greater part of its depth ; 
there is a marked zone of intermixture at the junction be- 
tween the warm water and the cold, and the water of the 
cold indraught is regularly stratified by gravitation ; so 
that in deep water the contour lines of the sea bottom are, 
speaking generally, lines of equal temperature. Keeping in 
view the enormous influence which ocean currents exercise 
in the distribution of climate at the present time, I think 
it is scarcely going too far to suppose that such currents, 
movement communicated to the water by constant winds, | 
existed at all geological periods as the great means, I had 
almost said the sole means, of distributing heat in the 
ocean, and thus producing general oceanic circulation ; 
they must have existed, in fact, wherever equatorial land 
interrupted the path of the drift of the trade winds. 
Wherever a warm current was deflected to north or 
south from the equatorial belt, a polar indraught crept in 
beneath to supply its place ; and the ocean consequently 
consisted, as in the Atlantic and doubtless in the Pacific 
at the present day, of an upper warm stratum and a lower 
layer of cold water, becoming gradually colder with 
increasing depth. Wherever such conditions existed it is 
plain that mere vertical oscillations must have produced 
very decided changes of climate, through only a small 
number of degrees, but still very marked if the oscillation 
affected merely a portion of the cold underlying water, 
but enormous if it were sufficient to raise or depress the 
bottom of the sea, the principal theatre of animal life, 
so as to shift it from the cold layer into the warm, or 
from the warm layer into the cold. 
One of the most striking phenomena connected with 
2 ims 
the distribution of heat in the North Atlantic is the case 
| of the Shailow including the Hebrides, Orkney and Shet- 
land Islands, and the Faroes, stretching westwards and 
northwards nearly to Iceland. The average depth is about 
500 fathoms, and the Gulf Stream, which has a depth 
in these latitudes in summer of from 600 to 7oo fathoms, 
occupies the whole of it, giving an abnormal temperature 
of something like 7°C. Owing to the peculiar confor- 
mation of the basin of the German Ocean, a tongue of 
cold water, with a bottom temperature of — 1° C. creeps 
into the valley between Scotland and Faroe, where it is 
overlaid by a stratum of Gulf Stream water, 150 fathoms 
thick. At the western mouth of the valley the cold water 
is banked in and retained by the water of the Gulf Stream, 
which is slowly passing the entrance of the gorge, giving 
a repetition, on a small scale, of the curious phenomenon 
described by Prof. Bache, off the coast of Massachusetts, 
as the “cold wall.” My colleague, Dr. Carpenter, has 
conveniently called these two neighbouring districts, 
where the thermometer indicates 7°C. and — 1° C. respec- 
tively, the warm and cold areas. A depression, affecting 
that region of 250 fathoms equal to that which admitted 
of the accumulation of post-tertiary shells on Moel Try- 
faen, would produce an extraordinary effect on its climate. 
In the first place, by mere subsidence, the Gulf Stream 
not reaching the bottom but flowing over a band of cold 
water, the temperature of the warm area would be re- 
duced to, say, 3° C., and that of the cold, by an indraught 
of deeper water from the north, to—2°C., but the Gulf 
Stream would no longer bank out the cold indraught 
from the north-east ; which, in that case, passing down a 
deep open channel from the deep soundings to the west 
of the Loffotens, would spread along the bottom on the 
west coast of Scotland and Iceland, and greatly reduce 
its temperature, and probably entirely alter its fauna. 
WYVILLE THOMSON 
NOTES 
WE have reason to believe that Professor Sir Wm. Thomson 
will be the next President of the British Association. 
WE learn that the Royal Commission on Scientific Instruction 
and the Advancement of Science, which has met regularly two 
days a week, have now adjourned over the recess. 
THE Royal Astronomical Society has issued a list of the mem- 
bers of the various learned Societies who propose to take part in 
the observations of the approaching total eclipse of the sun. 
WE learn from the last number of the Revue des Cours Sctentt- 
Jiques which has reached us—that for the 24th inst.—that on Mon- 
day last week the Paris Academy of Sciences continued, in comité 
secret, the discussion of Mr. Darwin’s nomination to fill the 
vacancy in the Zoological Section caused by the death of 
Purkinge. M. Milne-Edwards first spoke in his favour. While 
insisting on his own absolute opposition to evolutional doctrines, 
he rendered homage to the value of the special works of 
Mr. Darwin, especially the theory of the formation of coral 
islands. M. Elie de Beaumont also attested the value of 
this theory, and remarked that Mr. Darwin had done good work 
which he had spoiled by dangerous and unfounded speculations. 
He thought he should not be elected until he had renounced them. 
M. Emile Blanchard, who spoke for more than an hour, was 
very severe upon Mr, Darwin, styling him an ‘‘ amateur intelli- 
gent,” a remark capped by M. Elie de Beaumont (it is stated), 
who cried out, to the great indignation of M. de Quatrefages, 
“* C’est de la science mousseuse.” M. de Quatrefages promised to 
answer M. Blanchard point by point on Monday last. 
THE Archzeological Congress is now in full swing at Leicester, 
one of the most interesting towns and localities which it is pos- 
sible for such a Congress to visit. The proceedings commenced 
on Tuesday with an address presented by the Mayor and Corpo- 
ration, followed by visits to some of the objects of interest in the 
