;8o 



NATURE 



[August i6, 1894 



2000 fathom*:. This also is estimated from a very iosufiicient 

 number of soundings. 



The Atlantic, by far the best sounded ocean, has an area of 

 3l,ooo,c«o square miles, with a mean depth of about 2200 

 fathoms. 



The temperature of this huge mass of water is an interesting 

 point. 



The temperature of the surface is most important to us, as it 

 is largely on it that the climates of the different parts of the 

 world depend. This is comparatively easy to ascertain. We 

 know so much about it that we are not likely to improve on it 

 for many years. We are quite able to understand why countries 

 in the same latitude differ so widely in their respective mean 

 temperatures ; why fogs prevail in certain localities more than 

 others : and how it comes about that others are subject to 

 ttmpesluous storms. 



On the Litter point nothing has come out plainer from recent 

 discussion than the fact that areas where great differences of 

 surface temperature of the sea prevail are those in which storms 

 are generated. 



It is a mailer of observation that in the region south of Nova 

 Scotia and Newfoundland many of the storms which travel 

 over the .•\tlantic to this country have their rise. 



An examination of surface temperature shows that in this 

 region the variations are excessive, not only from the juxta- 

 position of the warm water of the Gulf Stream and the cold 

 waltrof ihe .\rctic current flowing southward inside of it, but 

 in the Gulf Stream itself, which is composed of streaks of warm 

 and colder water, between which differences of as much as 

 20° F. exist. 



The same condition^: exist south of the Cape of Good Hope, 

 another well-known birthplace of storms. Mere the Agulhas 

 current of about 70° F. diverted by the land pours into Ihe 

 mass of wa'er to the southward, colder by some 25^ and the 

 meeting-place is well known as mo5t tempestuous. 



South-east of the Rio de la Plata is another stormy area, 

 and here we find the same abnormal variations in surface 

 temperature. 



Yet another is found off the north-east coast of Japan with 

 the same conditions. 



These differences are brought about by the mingling of water 

 carried either by the flowing of a powerful current turned by 

 the land into a mass of water of different temperature, as is the 

 case off the Cape of Good Hope, or by the uprising of lower 

 strata of cooler water through a shallow surface stream, as 

 appears to be the case in the Gulf Stream. 



A remarkable point recently brought to light by the researches 

 of Mr. John Murray in Scotch lochs is the effect of wind on 

 the surface temperature. It has been observed that wind diiv- 

 ing oflT a shore drifts the surface water before it. This water is 

 replaced by the readiest means, that is to say, by water from 

 below the surface rising to take its place. -As the lower strata 

 are in all cases cooler than the surface a lowering of the tem- 

 perature results, and we find, in fact, that near all sea shores 

 off' which a steady wind blows the water is cooler than further 

 to seaward. 



This has an important bearing on coral growth, and explains 

 why on all western coasts of the great continents off which the 

 trade winds blow ue find an almost absolute dearth of coral, 

 while on the eastern coasts, on which warm currents impinge, 

 reefs abound, the coral animal flourishing only in water above 

 a certain temperature. 



Observ.nilons of the temperature of the strata of water 

 l>etween the surface and bottom have been of late years obtained 

 in many parts. Compared with the area of the oceans they 

 are but few, but our knowledge steadily increases every year. 



The subject of the vertical distribution of temperature has 

 not yet been thoroughly investigated in the light of the whole 

 of Ihe information which we now possess, but Ur. Alex. Buchan 

 has been for some time devoting his spare time to the task, and 

 it IS a heavy lal)our, for Ihe data obtained here and there over 

 Ihe world by different ships of all maritime nations are very 

 difficul' "> c"ll<?ct and to appraise, but I understand that before 

 long V Tve the result, which will prove very interesting, 



in ih • •: of the Challetii^rr %^x'\zi. 



'' ' '"' ' ' 'h.-it obcervations on Icmpera- 



■ care. In the first place the 



illy manufactured. They must 



li lesti, and Ihcymusi be carefully handled 



All observations arc not of the same 



NO. I J94, VOL. 50] 



value, and the discussion, therefore, presents considerable 

 difficulty and demands much discretion. 



In the meantime we can slate certain known facts. 



We have learnt that the depth of the warm surface water is 

 small. 



In the equatorial current between Africa and South America, 

 where the surface is of a temperature of 78°, at too fathoms it 

 is only 55°, a difference of 23°, and a temperature of 40° is 

 reached at 400 fathoms. In this region, so far as knowledge 

 goes, the fall in temperature as we descend is most rapid, but 

 generally speaking the same variations prevail everywhere. 



In Ihe tropical Pacific Ihe temperature falls 32° from the 

 surface, where it stands at 82°, to a depth of 200 fathoms, 40* 

 being reached at from 500 to 600 fathoms below the surface. 



Below the general depth of from 400 to 600 fathoms, the 

 temperature decreases very slowly, but there is considerable 

 variation in the absolute amount of it when we get to great 

 depths in different parts of the ocean. 



One of the most interesting facts that has been recognised is 

 that in enclosed hollows of the ocean the bottom temperature 

 is apparently much less than ihat of Ihe stratum of water at a 

 corresponding depth in the waters outside the submarine ridge 

 that forms the enclosing walls, separating them from deeper 

 areas beyond, and is, in all cases that have been observed, equal 

 to that on ihe ridge. From this fact we are enabled to supple- 

 ment our imperfect knowledge of depths, because if in a certain 

 part of an ocean we find that the temperature at great depths is 

 higher than we know exists at similar depths in waters appar- 

 ently connected, we can feel certain lhat there is a submarine 

 ridge which cuts off the bottom waters from moving along, and 

 that the depth on this ridge is lhat at which is found the 

 corresponding temperature in the outer waters. .Vs a corollary 

 we also .issume that the movement of water at great depths is 

 confined to an almost imperceptible movement, for if there was 

 a motion that we could term, in the ordinary acceptation of the 

 word, a current, it would infallibly surmount a ridge and pour 

 over Ihe other side, carrying its lower temperature with it. 



S. notable instance is the bottom temperaiure of the North 

 Atlantic. This is nowhere below 35° K., although the depths 

 are very great. Hut in the South .Xtlanlic at a depth of only 

 2800 fathoms the bottom temperature is but a little above 32° F., 

 and we are therefore convinced lhat somewhere between Africa 

 and South America, though soundings do not yet show it, 

 there must be a ridge at a depth of about 2000 fathoms. 



We also come to the same conclusion with regard to the 

 eastern and western portions of the South Atlantic, where 

 similar dift'erences prevail. 



Again, the few temperatures that have been obtained in the 

 eastern South P.acific show a considerable difference from those 

 in the South .Atlantic, and we are compelled to assume a ridge 

 from the Falkland Islands to Ihe Aniarctic continent. 



It is interesting that the investigation into the translation of 

 the great seismic wave caused by the eruption of Krakatoa in 

 1S83 led to a similar and entirely independent conclusion. The 

 wave caused by the explosion in the Straits of Suntia reached 

 Cape Horn, where by good chance a French meteorological 

 expedition had erected an automatic tide gauge, but instead 

 of one series of waves being marked on Ihe paper there were 

 two. A little consideration showed lhat Ihe South Pole having 

 directly interposed between .Sunda .Siraits and Cape Horn, the 

 waves diverted by the land about the pole would arrive from 

 both sides. 



One wave, however, made its appearance seven hours before 

 the other. 



Study showed that the earliest wave coincided in time with a 

 wave travelling on the Pacific side of the pole, with a velocity 

 due to the known depth, while the later wave must have been 

 retarded in its journey vu'i the South Atl.intic. The only 

 possible explanation is that the wave had been impeded by 

 comparatively shallow water. 



The evidence from bottom temperature was Ihen unknown, 

 and thus does one branch of investigation aid another. 



In the Western I'acilic Ihe water is colder, a few bottom tem- 

 peratures of a Utile over 33° F. having been found in llie dtcp 

 trough east of the Tonga Islands ; but ihe North Pacific, though 

 the deeper ocean — of enormous area and volume — is apparently 

 again cut off" by a submarine ridge. The notlh-w•e^lcrn part 

 of the Indian Ocean is for similar reasons assumed to he 

 dividcil fiom ihe main body, the shallower water probably 

 running from the Seychelles to the Maldive Islands. 



