March 10, 1870| 
NATURE 
489 
low depths of from 350 to 650 fathoms—the last-named being 
the greatest depth to which dredging had been carried in 1868. 
The weather, during nearly the whole of the Porcupine expe- 
dition, was as favourable to its work, as during the greater part 
of the Lightning expedition it had been unfavourable ; and“the 
results obtained not only far exceeded the most sanguine expec- 
tations of those who had promoted it, but may be said, without 
exaggeration, to be such as no previous scientific exploration of 
so limited an extent and duration is known to have yielded. 
The results of the temperature-soundings will be first stated, 
with their bearing on the doctrines advanced in the former dis- 
course as probable inferences from the observations made during 
the Lightning expedition. These observations indicated that two 
very different submarine climates exist in the deep channel which 
lies E.N.E. and W.S.W. between the North of Scotland and 
the Faroe Banks ; a minimum temperature of 32° having been 
registered in some parts of this channel, whilst in other parts of 
it, at the like depths, and with the same surface temperature 
(never varying much from 52°), the minimum temperature 
registered was never lower than 46°,—thus showing a differ- 
ence of 14°. It could not be positively asserted that these 
minima are the bottom-temperatures of the Areas in which 
they respectively occur: but it was argued that they must 
almost necessarily be so :—first, because it is highly impro- 
bable that sea-water at 32° should overlie water at any higher tem- 
perature, which is specifically lighter than itself, unless the two 
strata have a motion in opposite directions sufficiently rapid to be 
recognisable; and secondly, because the nature of the animal life 
found on the bottom of the cold-area, which consists of quartzose 
sand including volcanic particles, exhibited a marked correspon- 
dence with its presumed reduction of temperature, whilst the 
sea-bed of the warm area is essentially composed of Globigerina- 
mud, and the animal life which it supports is characteristic of 
the warmer-temperate seas. 
This conclusion, itis obvious, would not be invalidated by any 
error arising from the effect of pressure on the bulbs of the 
thermometers ; since, although the actual minima might be, as 
was then surmised, from 2° to 4° below the recorded minima, the 
difference between temperatures taken at the same or nearly the 
same depths would remain unaffected. 
The existence in the cold area, of a minimum temperature of 
32°, with a Fauna essentially Boreal, could not, it was argued, 
be accounted for in any other way than by the supposition of an 
under-current of Polar water coming down from the north or 
north-east : whilst, conversely, the existence in the warm area, of 
a minimum temperature of 46”, extending to 500 or 600 fathoms’ 
depth, in the latitude of 60° (being at least 8° above its isotherm), 
together with the warmer-temperate character of its Fauna, 
seemed equally indicative of a flow of equatorial waters from the 
south or south-west. 
It was further urged that if the existence of two such different 
submarine climates in close proximity can only be accounted 
for on the hypothesis of an Arctic stream and an Equatorial 
stream running side by side (the latter also spreading over the 
former in consequence of its lower specific gravity), these 
streams are to be regarded (like the Gulf Stream) as particular 
cases of a great general Oceanic Circulation, which is continu- 
ally bringing the water cooled-down in the Polar regions into 
the deepest parts of the Equatorial ocean-basins, whilst the 
water heated in the Equatorial regions moyes towards the 
poles on or near the surface. Such a circulation was long 
since pointed out to be as much a physical necessity, as that 
interchange of A‘v between the Equatorial and Polar regions 
which has so large a share in the production of winds; but 
whilst physical geographers remained under the dominant idea 
that the temperature of the deep sea is everywhere 39°, they 
could not fully recognise its importance. 
These doctrines have been fully tested by the very numerous 
and careful temperature-soundings taken in the Porcupine expedi- 
tion; and the result has been not merely to confirm them in 
every particular—so that they may now take rank as estab- 
lished facts,—but also to show that a temperature 23° below 
the freezing-point of fresh water may prevail over the sea-bed 
in a region far removed from the Polar, and that even this 
extreme reduction is by no means antagonistic to the existence 
of animal life in great variety and abundance. 
All the temperature-soundings of the Porcupine expedition were 
taken with thermometers protected from the effects of pressure by 
the enclosure of the bulb of each instrument in an outer bulb, sealed 
round the neck of the tube; about three-fourths of the interyening 
space being filled with spirit, but a small vacuity being left, by which 
any reduction in the capacity of the outer bulb is prevented from 
communicating pressure to the inner. This plan of construction, 
which was suggested by Prof. W. A. Miller, has been so suc- 
cessfully carried into practice by Mr. Casella, that thermometers 
thus protected have been subjected to a pressure of three tons on 
the square inch, in a testing-machine devised for the purpose, 
without undergoing more than a very slight elevation, of which 
a part, at least, is attributable to the heat given out by the com- 
pression of the water in which they were immersed : whilst the 
very best thermometers of the ordinary construction were affected 
by the same pressure to the extent of 8° or 10°, the elevation in 
some instruments reaching as muchas 50° or 60°.* Two of these 
protected Miller-Casella thermometers were used in each obser- 
vation, and they always agreed within a fraction of a degree. 
The same pair was used throughout the expedition; and not- 
withstanding that they were used for 166 separate observations, 
in which they travelled up and down nearly 100 miles, they came 
back in perfectly good order; a result mainly due to the care 
with which they were handled by Captain Calver. It may be 
affirmed with great confidence that the temperatures which they 
indicated were correct within 1° (Fahr.) ; anapproximation quite 
near enough for the scientific requirements of the case. 
In order to connect the work of the Porcupine with that of 
the Lightning expedition, it will be desirable to commence 
with the third cruise of the former, in which a detailed survey 
was made of the area traversed in the preceding year by the 
latter. In this cruise bottom-soundings were taken at thirty- 
six different stations, at depths varying from 100 to 767 fathoms ; 
of these, seventeen were in the cold area and fourteen in the 
warm, whilst five exhibited intermediate temperatures, in ac- 
cordance with their border position between the two. In order 
to ascertain whether the minimum temperatures thus obtained 
were really the temperatures of the bottom, serial soundings were 
taken at three stations, of which one was in the warm area 
and two in the cold—the temperature at different depths between 
the surface and the bottom being ascertained by successive 
observations, at the same points, at intervals of 50 or 100 fathoms. 
All these results agreed extremely well with each other; and 
they closely accorded with the fifteen observations made in 
the Lightning expedition, when the requisite correction for 
pressure (from 2° to 3° according to the depth) was applied to 
the latter. 
The following general summary of these results brings into 
marked contrast the conditions of the warm and cold areas, 
which occupy respectively the W.S.W. and E.N.E. portions of 
the Channel between the north of Scotland and the Faroe Is- 
lands, and lie side by side in its midst. 
The surface-temperature may be said to be everywhere nearly 
the same, viz. 52°; the variations above and below this being 
attributable either to atmospheric differences (as wind, sunshine, 
&ce.) or to difference of latitude. Alike in the warm and the 
cold areas there was a fall of from 3° to 4° in the first 50 
fathoms, bringing down the temperature at that depth to 48°. A 
slow descent took place nearly at the same rate in both areas 
through the next 150 fathoms ; the temperature in the warm 
area at the depth of 200 fathoms being 47°, whilst in the cold it 
was 45°7°. It is below this depth that the marked difference 
shows itself. For whilst in the warm area there is a slow and 
pretty uniform descent in the next 400 fathoms, amounting to 
less than four degrees in the whole, there is in the cold area, a 
descent of fifteen degrees in the next 100 fathoms, bringing down 
the temperature at 300 fathoms to 30°5°. Even this is not the 
lowest; for the serial soundings taken at depths intermediate 
between 300 and 640 fathoms (the latter being the greatest 
depth met with in the cold area, midway between the Faroe 
and the Shetland Islands) showed a further progressive 
descent; the lowest bottom - temperature met with being 
296°. Thus, while the temperature of the superficial stratum 
of the water occupying the cold area clearly indicates its 
derivation from the same source as the general body of water 
occupying the warm area, the temper ture of the deeper stratum, 
which may have a thickness of more than 2,000 feet, 
* See Prof. W. A. Miller’s ‘‘ Note upon a Self-Registering Thermometer, 
adapted to Deep Sea Soundings,” in “ Proceedings of the Royal Society,” 
June 17, 1869.—The same principle had been previously applied in thermo- 
meters constructed under the direction of Admiral Fitzroy; the space 
between the two bulbs, however, being occupied with mercury instead of 
spirit. Owing, however, to some imperfection in their construction, their 
performance was not satisfactory, and they were found very liable to 
fracture, 
