tures, such as 33, 32-2, and 32 degrees. But at the like depth in another part of this channel, the soundings, as marked in the upper part of the table, show a temperature of 45 to 48 degrees. Here was a very marked and curious contrast; for within a short distance of each other, in one instance only twenty miles apart, we found two very different climates at the same depth.

bers we may say that at 800 fathoms the part of the channel, very low temperapressure of a column of water is one ton upon every square inch; therefore, at 2,400 fathoms, which was nearly the greatest depth to which our soundings extended, the pressure is three tons to the square inch; and that is just the pressure to which our thermometers had been tested. Therefore we know that we had within a degree (we always used two thermometers) the real temperature of the bottom of the ocean. Now I shall show you what Now the existence of these two very very curious and important information different climates showed itself, when we we derived from ascertaining the tempera- carefully worked it out afterwards, in two ture, not only of the bottom of the ocean very distinct kinds of animal life, and in at different depths, but also of different two very distinct kinds of deposit on the portions of the column of water in going down to the bottom. This we ascertained by letting down our thermometers to a certain depth, and then taking them up; then letting them down to a greater depth; and so on. In that manner we got what I term "serial soundings"- that is, a series of temperatures of different depths in the same spot; and those corresponded very closely indeed with the bottom temperatures that we got at like varying depths. As a rule, the lowest temperature was always the bottom temperature. I shall presently explain to you how this comes

to pass.

bottom of the ocean. I will first show how our next year's work in the same region filled up and completed this inquiry, and gave us some very curious points in addition. You may imagine with what interest we went over this ground again, provided with our superior thermometers; for the first year's work was done with the old thermometers, only the depths were not so great as seriously to interfere with their performance. And you will observe that whether those thermometers had been in error or not (which we did not know till we tried), the same effect would be produced in raising the mercury at 500 fathoms, whether it was in the warm or the cold area; so that the difference of the warm and the cold-between about 32 and 47 degrees would be just the same. These themometers having been a couple or three degrees too high- as they proved to be we found that the temperature of the first year, which had been 32o, became 30°, and that which had been 47° was really 45°. But the difference of 15 degrees was exactly the same; and the conclusions at which we had originally arrived in regard to it were verified in the very careful, numerous, and elaborate inquiries which we prosecuted over this area the next year. The most remarkable contrasts of bottom-temperature were shown at different depths on the southern slope of the channel. Thus, at a depth of 190 fathoms the temperature was 48°.6; whilst only eight miles to the north, where the depth had increased to 445 fathoms, the thermometer sank to 30°-1; thus showing a difference of bottom-temperature to the amount of 18° within that short distance, with a difference of only 255 fathoms in depth.

Our first expedition was a very short one. We had very bad weather in a very stormy region, between the North of Scotland and the Faroe Islands, and we were not able to make many soundings or many | dredgings; and yet, by a piece of extraordinary good fortune, the temperatures of the soundings that we obtained were as curious as any we have obtained since; and they suggested to me a general doctrine in regard to Oceanic Circulation, that all our subsequent researches have tended to confirm. The general facts of the case you will see by this map and the table by the side of it. Here is the north point of Scotland, the Orkney Islands, and Stornoway, the little port of the Hebrides from which we started. Here are the Faroe Islands. This dotted line is what is called the "hundred fathom line" - that is, the line which bounds that curious platform, so to speak, of which the British Islands constitute the highest part. So that dotted line around the Faroe Islands represents water which is under 100 fathoms. Now between this and the Shetland Islands is a deep channel reaching down to 600 fathoms, which is a depth nearly Again, we took what I have called "seequal to the height of Snowdon. Our rial soundings; that is, we let down our soundings in the first expedition were thermometers at different depths, for inmade along this line, where we found, in a` stance at 50 fathoms, then at 100, then at

150, then at 200, then 250, and so on every 50 fathoms; and the results we got are shown in the diagram,* which is so constructed that a curve indicates the descent of the thermometer, and the depths are expressed by the horizontal figures, which run from 50 to 100, 150, &c., marking every 50 fathoms.

the Polar area; but over it there was another stream proceeding north-east, consisting of water warmer than the normal water of the latitude; for this last would have been about 40°, while the temperature of the surface was about 529, and even at 500 fathoms it only sank to 45°.

Now, then, what is the meaning of this? In all this area, whether it was warm or When I speak of a "stream" and "flowcold at the bottom, we found nearly the ing," you must understand that there is same surface-temperature a very curi- nothing like a visible movement. I say ous fact. If we went north it was a little that this cold stream must be flowing, beless, and if south a little more; but about cause if it were not flowing it could not 52 degrees was the average. We found retain its temperature; it would soon give that in all parts of this area the descent up its warmth to the water above. It is through the lowering of the thermometer quite a physical necessity that it should in the first 150 fathoms was the same; be in movement; and of course if it is in and in the warm area, when we got below motion, only by coming from the Polar 150 fathoms, there was very little more area could it have brought this cold temlowering of the temperature. You see perature with it, for at the bottom it was that the line in the warm area continues about 29 1-2 degrees. You are aware nearly horizontal till we pass about 500 that 32 degrees is the freezing point of fathoms; but from 150 to about 500 fath- fresh water; but it is not the freezing oms there was very little lowering of the point of salt water. Sea water freezes at temperature, the reduction being from 52° about 27°; if it is kept very still it will at the surface to about 45° at 500 or 600 not freeze till 25°; and there is a most fathoms. But now see what takes place important difference in the condition of in the cold area. This upper line, which sea water and fresh water as regards temat 100 fathoms is but a little below the perature below 392 degrees. You all other, begins to drop rapidly, so that at know perfectly well that when a frost acts 200 fathoms it is very decidedly below; and upon the surface of a lake, river, or pond, then it goes down still more rapidly, so the water freezes on the surface; and if that within 100 fathoms it dropped about you put down a thermometer into the 15 degrees; and all the water in that par- water below, you will find that its temperticular sounding below 300 fathoms was ature is about 39 degrees. Now, why is of a temperature below the freezing point this? You know that the ordinary rule of fresh water. The bottom was there of the contraction of water is that it struck at 384 fathoms; but in another shrinks, just like the mercury in a therpart we got a much deeper sounding, mometer, with cold, and expands with down to 640 fathoms, which was taken at heat. As it shrinks it becomes denser, a point a good deal north: there the sur- and therefore heavier, bulk for bulk; conface-temperature lowered to between 49 sequently when a low atmospheric temand 50 degrees; it went down in much perature is acting upon the surface of a the same manner as in the other, until it pond or lake, the water as it is cooled at got to 350 fathoms, which was below the the surface becomes heavier and goes freezing point of fresh water; and from down. So it keeps on going down, while that point to the bottom (640 fathoms) the warmer water beneath, which is lightwas a river, so to speak, of glacial water er, comes up to the surface, till the whole nearly 2,000 feet deep - below the freez-is cooled down to about 39-2 degrees; ing point of fresh water. Now that was but then continued cold does not produce the very curious fact which our investigations of this channel between the Faroe Islands and Orkney and Shetland brought to our knowledge. That channel I have been accustomed to designate the "Lightning Channel," "Lightning" being the name of the vessel assigned to us in our first expedition. This cold stream must have come straight into this channel from

We regret that we cannot reproduce the diagram, but think the text will be sufficiently intelligi. ble without it. LIVING AGE.

the same effect, for below 39-2 the water begins to expand again, the greater cold making it lighter instead of heavier; consequently the water which is cooled to below 39-2 degrees remains on the surface, and by continued exposure to the action of the cold atmosphere it freezes and forms a layer of ice. But that is not the case with salt water. Sea water continues to contract down to its freezing point; the more it is cooled the heavier it becomes, because its bulk diminishes; it therefore

sinks in proportion to its degree of cold-can we give of it? How does it come to ness; and in this manner it is that the be there? and how does it come to retain coldest water nearly always comes to be at the bottom.

its low temperature? Now I think it may be said with perfect certainty, that it could This has a most important relation to not long retain its low temperature unless the doctrine of Submarine Climate. I it was continually supplied from the Polar have shown you here a sort of little com- area. I will show you how this supply pact pocket edition of a set of phenomena, takes place. Here, for instance, in this which, as I am now going to explain, prob- Lightning Channel, we found that we could ably prevails over the whole of our great distinctly trace it along near to the corner Oceans. In our soundings a few months of the Faroe Banks; and though we had ago on the coast of Spain and Portugal, not the means (which I hope we may at we came upon this fact; the surface tem- some future time) of measuring its moveperature was very high, about 65 degrees; ment, yet by the nature of the bottom we in the first 100 fathoms we lost about 10 felt pretty sure that it was a running degrees of this, which we may call the stream, for the pebbles there instead of super-heating of the surface, produced by being angular were round-which you the powerful rays of the midsummer sun. know is a distinct indication of a current. Then the temperature from a depth of 100 Well, then, we have every reason to believe fathoms down to 800 lowered very slowly, that this stream ran on and discharged itjust as it does in the "warm area; " so that self into the great Atlantic basin. For at 800 fathoms it only got down to 49 de- about 100 miles to the westward of this grees. But in the next 200 fathoms, be- there is a deep slope, going down to 1,500 tween 800 and 1,000, there was a loss of 9 or 2,000 fathoms; and thus it would be degrees, the temperature falling to 40; in one of the feeders, so to speak, of the another 100 fathoms, it fell another degree; great mass of Polar water in the Atlantic and over the deeper soundings which we basin. Then between the Faroe Islands took in the previous year, extending down and Iceland there is a shallow bank; but to 2,435 fathoms, or nearly three miles between Iceland and Greenland, again, a depth about equal to the height of Mont there is a wide and deep channel, through Blanc-we got a temperature as low as which a very large mass of Polar water 36 1-2 degrees; and still lower tempera- can come down. And though no tempertures have been obtained elsewhere, even ature-soundings have yet been made (so near the Equator. The recent tempera- far as I am aware) in this channel, yet the ture-soundings made by Commander Chim- character of the bottom, as shown in the mo with the "protected" thermometers," Bull-dog soundings, corresponded so in Lat. 3° S. and Long. 95° E. have given closely with that of our own cold area, as 35.2 as the bottom-temperature at 1,806 to justify the belief that the deep water is fathoms, and 33°.6 at 2,306 fathoms. Here, glacial. Now water cannot be always then, you see we have in our great Oceans flowing out of the Polar basin, without a condition just comparable with that water from some other source flowing into which we found in the Lightning Channel: it; so that if there is such an outflow at its first we have an upper stratum of warm bottom, the circulation must be completed water; then we have what I have desig- by a constant inflow of surface-water. nated a "stratum of intermixture;" but While, then, the deeper water is coming below 1,000 fathoms, the water ranges from the Pole, there must be surface-water from 39° nearly down to freezing point. going towards the Pole.

Near the Pole it is quite down to freezing You have all heard of the Gulf Stream. point; but when it is nearer the Equator, It is a great mass of water issuing from where it has had a long way to flow from the Pole, it will have acquired a certain slight degree of warmth; but still, you see, the finding a temperature of 33 or 35 degrees under the Equator, shows clearly that that water must have come from one or other of the Poles.

Let us now enquire what account can be given of this remarkable phenomenon. Here we have in the deep Oceanic basins this layer of water extending more than a mile deep-water which must have been derived from the Polar area. What account

the Gulf of Mexico through the channel between the peninsula of Florida and the Bahama Islands, and flowing in a northeasterly direction. The very powerful current that passes through that narrow channel, flows at first at the rate of three or four miles an hour in a direction which carries it towards the Banks of Newfoundland and the Azores; and it is popularly believed to flow on towards the northern coast of the British Isles, and thence to Spitzbergen, Iceland, and even Nova Zembla. Now I have every reason to believe,

of the Gulf Stream. It is known that Polar water also underlies the Gulf Stream; for if you send the thermometer sufficiently deep, you find a very low temperature beneath this extraordinary surface-current, even in the Florida channel.

from careful inquiries lately made, that this Gulf Stream really has not much to do with the phenomena of which I have been telling you, and that its influence pretty much ceases not far to the eastward of the banks of Newfoundland. The Gulf Stream is part of the horizontal circulation I have adverted to the Gulf Strean, bein the North Atlantic. I think you will cause I want to show the important influeasily understand the difference between a ence of the upper movement of warm horizontal circulation and a vertical_circu-water of which I previously spoke, which lation. Look at the wind ruffling the sur- is quite independent of the Gulf Stream. face of a pond. It blows the water in a Suppose that the narrow peninsula of particular direction, and produces little rip- Mexico, or the narrowest part of it, the ples. If it drives away the water, of course Isthmus of Panama, which connects North water must come in to fill up its place and South America, were broken through from some other part of the pond. That as it will be in course of ages by the is a horizontal circulation; and the hori- action of the sea-so that a free course zontal circulation in the Atlantic is pro- should be given to the Equatorial current; duced in this way. The Trade Winds are it would then go right through into the always blowing between the tropics from Pacific Ocean, and we should have no Gulf east to west; they move along an enor- Stream at all. But even in that case, I mous mass of water, excesssively heated think our climate would not suffer so much by the action of the sun, constituting the as most persons believe; because though Equatorial Current, and drive it into the we should lose some portion of our warm Gulf of Mexico; it circulates there, and south-westerly winds, this constant flow comes out from the Florida channel as a of warm water which is taking place in rapid current. But that rapid current, the whole mass of the North Atlantic — there is strong reason to believe, is not as from the southerly area directly towards deep as is commonly supposed; and the the north and north-east, so as to enter the amount of the heat it carries has been Polar area-will still continue, carrying very much over-estimated. As it passes with it a temperature which, taken altoalong the coast of the United States (sep-gether, is very much greater than that of arated from it by a current of cold water the Gulf Stream. For the last we know that comes down from the north), it definitely of the Gulf Stream shows that spreads itself out, becoming proportionally it is thinned off to a layer of certainly not thinner, and at the same time slackening more than 50 fathoms, and perhaps less, in its rate of movement. Its temperature progressively falls, especially in winter; and when the stream is reduced to a mere surface-film, it cannot retain a temperature much above that of the atmosphere. About half of it, when it comes to the Azores, or Western Islands, turns round again, goes near the African coast, and returns into the Equatorial Current; completing therefore one portion of the circulation I have spoken of. The other half goes on past the Banks of Newfoundland; there it meets the surface of the Arctic stream, which breaks it up or "inter-digitates" with it this word expressing an action like that of passing one set of fingers through another. I admit that a portion of the Gulf Stream goes north, but the greater part of it is stopped and cooled by this Polar current coming down; and it is the southward continuation of this cold surface-current from the coasts of Greenland and Labrador, which gives the low winter temperature to the sea- But you will ask, and very properly, board of the United States, and which "What evidence have you of this moveforms the complement of the northern halfment?" and "What produces this move

and reduced to a temperature of about 65 degrees; whereas this great slowly-moving mass of water carries a temperature higher than the temperature of the latitude down to 500 or 600 fathoms' depth; and as the surface is cooled, warm water from below will come up to take its place; and in this manner will carry into the Polar area a great body of heat derived from the general surface of the Temperate and Tropical oceans. And this I believe has taken place in all Geological periods, quite irrespective of any such local accidents as those which produce the Gulf Stream. There must have been in all Geological periods a movement of this warmer water from the Equatorial towards the Polar area, and conversely (and this is most important geologically) a movement of cold water in the depths of the oceanic basins, from the Polar towards the Equatorial area, bringing with it the characteristic animals of the Polar climate.

ment?"

Now, the evidence of such a to be influenced by what is called the "in" movement lies in the fact that cold water ternal heat of the earth," which you expecould not remain cold water at the bottom rience when you go down into a deep coalof these Oceanic basins, if the supply were pit, for instance, or which shows itself in not kept up from the cold basins at the the hot water from very deep springs; and Poles. I will give you an illustration. at that depth they are covered with a layer We were at work this last summer in the of earth which is a sufficiently bad conMediterranean; and we found its condi- ductor to prevent their being much inflution most curiously different in regard to enced by season changes; they therefore temperature from the condition of the take the permanent temperature of the crust Atlantic. The Mediterranean is a basin of the earth, and that permanent temperawhich, to use a Scotch word, is "self-con- ture in Central Europe is found to be about tained;" it is shut in almost entirely, the 51, 52, or 53 degrees. Now I found that Strait of Gibraltar being its only commu- there was a cave in a little island which we nication with the outside; and that Strait visited between Sicily and the coast of is so shallow at its outlet, that no commu- Africa, which has the reputation of being nication between the deep water of the Mediterranean and that of the Atlantic can possibly take place. The Mediterranean goes down in some parts to a depth of 2,000 fathoms: we ourselves sounded to above 1,700, that is from about 11,000 to 12,000 feet. We found the surface very hot, being there in August and September: the temperature of the surface of the sea rose to 78 degrees in some instances. But we found that hot temperature limited to a very shallow layer indeed; we lost 10 or 15 degrees of that heat in 30 fathoms; at a depth of 30 fathoms we found the temperature perhaps 63, or sometimes as low as 60 degrees. Then a further loss of temperature would be experienced in going down to 100 fathoms. At that depth we came almost invariably to 54 or 55 degrees; and whatever was the temperature at 100 If, then, it were not for the vertical circufathoms, that it was down to the very bot-lation of the water in our great Oceanic tom; depth there made no difference at all; if it was 55 degrees at 100 fathoms it would be 55 at 1,700 fathoms; and if it was 56 degrees at 100 fathoms it would be the same at the greatest depth. There was a little difference in different parts of the area, which can be explained by local causes; but, as a rule, whatever the temperature was at 100 fathoms, that it was at the bottom.

Now what is the cause of this difference between the Mediterranean and the Atlantic? In a basin of very great depth, like the Mediterranean, why should the temperature be thus curiously uniform? Simply because it is entirely cut off from this General Oceanic Circulation, so that the water takes the temperature of the crust of the earth at that particular part. I will give you some curious evidence that such is the case. Thermometers buried deep in the soil in Central Europe are found to vary very little indeed during the different seasons. At about 20 or 30 feet from the surface they are not deep enough VOL. XXV. 1173

LIVING AGE.

icy cold." I was very anxious to visit it, but circumstances did not allow of our doing so; however, I had afterwards the opportunity of learing that the temperature of this cave is 54° through the whole year. Then a Maltese gentleman, the collector of customs at Valetta, a very intelligent and well-informed man, told me that it is the practice among the natives to let down their wine to cool it in the deep tanks which they have excavated in the rock. I asked him if he happened to know the temperature in these deep tanks, and he said, “Yes, it is 54 degrees." So you see we have several pieces of confirmatory evidence, showing us that the bottom-water of the Mediterranean takes exactly the temperature of the crust of the earth on which it rests.

basins, the temperature of the bottom of the Atlantic would be 55°, like that of the Mediterranean within the Strait of Gibraltar. But see what we get a little outside that basin. Near the coast of Spain, only 100 or 200 miles from Gibraltar, we found the temperature 49° at 800 fathoms, and we got down to 39° at 1,100 fathoms. Now this shows perfectly clearly that such. a low temperature could only be sustained by a constant flow of water from the Polar basin towards this southern region. Then, as I have shown you, that outflow could not continue without an inflow into the Polar basin. And that brings me to show you what is the force that maintains this circulation. It is produced by the continual cooling of the water which flows into the Polar area; for it becomes heavier and falls to the bottom, displacing the water previously there, pushing it away as it were. Thus, there is a constant sinking of water in the Polar area exposed to a much colder atmosphere; for every fresh layer of water that comes in from the