August 31, 1905 J 



NA TURE 



451 



The other recent event in geographical exploration is the 

 result of the expedition to Lhasa. It was an unexpected 

 solution of this long-desired knowledge that it should come 

 from political necessities and by means of a Government 

 mission. The many ardent travellers who have dreamed 

 of one day making their way in by stealth have thus been 

 disappointed, but our knowledge is now fuller than could 

 otherwise have been gathered. 



The most important fact is the revelation of the fertility 

 of a large part of Southern Tibet. Much has been added 

 to topographical knowledge, but the route maps of the 

 secret Indian native surveyors already had given us a rough 

 knowledge of the country on the road to Lhasa. It was 

 not, however, realised how great was the difference between 

 the aridity of the vast regions of the north, known to us 

 from the travels of men of various nationalities, and the 

 better-watered area in the south, though from the great 

 height of the plateau — some 12,000 feet — the climate is very 

 severe. The upper course of the Brahmaputra has been 

 traced by Captain Ryder, but, unfortunately, a political 

 veto was placed on the project to solve the interesting 

 problem of how this great river finds its way to the Indian 

 plains, and this still remains for the future to unravel. 



Of the ocean, which has been my own particular study 

 for many years, and on which alone I feel any special 

 qualification to speak, I have said but little, for the reason 

 that when presiding over this Section on a former occasion 

 I took it for my theme, but there are a few points re- 

 garding it which I should like to bring to your notice. 



It is of the ocean, more than of any other physical 

 feature of our globe, that our knowledge has increased of 

 late years. Forty years ago we were profoundly ignorant 

 even of its depth, with the exception of a few lines of 

 soundings then recently taken for the first submarine tele- 

 graph cables, and consequently we knew nothing of its 

 real vast bulk. As to the life in it, and the laws which 

 govern the distribution of such life, we were similarly 

 ignorant, as of many other details. 



The Challenger expedition changed all this, and gave an 

 impetus to oceanographic research which has in the hands 

 of all nations borne much fruit. 



Soundings have been obtained over all parts of the seas, 

 even in the two polar seas ; and though much remains to 

 be done, we can now form a very close approximation to 

 the amount of water on our earth, whilst the term " un- 

 fathomable ocean " has been shown to have been based on 

 an entire misconception. Biological research has also re- 

 vealed a whole world of living forms at all depths of the 

 existence of which nothing was known before. 



In my former Address, eleven years ago, I gave many 

 details about the sea, of which 1 will only repeat one — 

 which is a fact that everyone should know — and that is, 

 that the bulk of the ocean is about fourteen times as 

 great as that of the dry land above water, and that if the 

 whole of that land were thrown into the Atlantic Ocean it 

 would only fill one-third of it. 



Eleven years ago the greatest depth known was 4700 

 fathoms, or 28,000 feet. We have since found several places 

 in the Pacific vifhere the depth is nearly 5170 fathoms, or 

 31,000 feet, or somewhat higher than Mount Everest, which 

 has been lately definitely shown to be the culminating 

 point of the Himalayas. These very deep parts of the 

 ocean are invariably near land, and are apparently in the 

 shape of troughs, and are probably due to the original 

 crumpling of the earth's surface under slow contraction. 



The enormous area of the sea has a great effect upon 

 climate, but not so much in the direct way formerly 

 believed. While a mass of warm or cold water off a coast 

 must to some extent modify temperature, a greater direct 

 cause is the winds, which, however, are in many parts the 

 effect of the distribution of warm and cold water in the 

 ocean perhaps thousands of miles away. Take the United 

 Kingdom, notoriously warm and damp for its position in 

 latitude. This is due mainly to the prevalence of westerly 

 winds. These winds, again, are part of cyclonic systems 

 principally engendered off the coasts of Eastern North 

 America and Newfoundland, where hot and cold sea- 

 currents, impinging on one another, give rise to great 

 variations, of .temperature and movements of the atmo- 

 sphere which start cyclonic systems travelling eastwards. 



NO. 1870, VOL. 72] 



The centre of the majority of these systems passes north 

 of Great Britain. Hence the warm and damp parts of them 

 strike the country with westerly winds, which have also 

 pushed the warm 'water left by the dying-out current of the 

 Gulf Stream off Newfoundland across the Atlantic, and 

 raises the temperature of the sea off Britain. 



When the cyclonic systems pass south of England, as 

 they occasionally do, cold north-east and north winds are 

 the result, chilling the country despite the warm water 

 surrounding the islands. 



It only requires a rearrangement of the direction of the 

 main Atlantic currents wholly to change the climate of 

 Western Europe. Such an arrangement would be effected 

 by the submergence of the Isthmus of Panama and adjacent 

 country, allowing the Equatorial Current to pass into the 

 Pacific. The gale factory of the Western Atlantic would 

 then be greatly reduced. 



The area south of the Cape of Good Hope is another 

 birthplace of great cyclonic systems, the warm Agulhas 

 Current meeting colder water moving up from the Polar 

 regions ; but in the Southern Ocean the conditions of the 

 distribution of land are different, and these systems sweep 

 round and round the world, only catching and affecting the 

 south part of Tasmania, New Zealand, and Patagonia. 



In 1894 I spoke of the movements of the lower strata 

 of water in the sea as a subject on which we were only 

 beginning to get a little light. Since that year we have 

 learnt a little more. It is a common idea that at the 

 bottom of the sea all is still ; but this is a mistake, even 

 for the deepest parts, for the tidal influence reaches to the 

 bottom and keeps every particle in motion, though such 

 motion is quiet and slow. 



Near the shore, however, though still in deep water, the 

 movement may be considerably increased. Cases have 

 occurred in late years where submarine cables have broken 

 several hundred fathoms deep, and when picked up for 

 repair it has been found that the iron wire covering has 

 been literally rubbed away as by a file. This can only be 

 the result of an undercurrent along the bottom moving the 

 cable to and fro. Such a current might be caused by a 

 submarine spring, for there is no doubt that much fresh 

 water finds its way into the ocean in this fashion, but it 

 is more probably generally an effect of acceleration of the 

 tidal movement due to the rising slope of the continent. 



In connection with this, further facts have come to light 

 in the course of recent marine surveys. 



Many isolated shoal spots in the great oceans have figured 

 in our charts, the results of reports by passing sailors 

 who have said they have seen breakers in fine weather. 



Such places are the terror of seamen, and it is part of 

 the duty of surveying ships to verify or disprove them. 

 Very much has been done in the last eighteen years, with 

 the result that the majority of them have, as dangers, dis- 

 appeared. In many cases, however, a bank has been found, 

 deep in the ordinary acceptation of the word, but must less 

 deep than the surrounding sea — solitary ridges, in fact, 

 rising from the ocean floor. Frequently, in examining these 

 banks in search of shoaler spots, breakers have been re- 

 ported and recognised as such on board the surveying ship 

 from a distance, but on approach they have proved to be 

 small overcurls caused by tide ripplings, and the depth 

 of water has proved to be several hundred fathoms. 

 These ripplings are clearly caused by the small tidal 

 motion in the deep water, generally in these cases 

 of more than 2000 fathoms, meeting the slope of 'he 

 submerged mountain range, being concentrated and ac- 

 celerated until the water finally flows up the top of the 

 slope as a definite current, and taking the line of least 

 resistance, that to the surface, makes itself visible in the 

 shape which we are accustomed to associate with com- 

 paratively shallow water. 



These cases form remarkable instances of the manner in 

 which e.xtensive motion of water may arise from very small 

 beginnings. 



An observation I was anxious to make in 1894 has been 

 successfully carried out since. This was to ascertain 

 whether there was any permanent undercurrent in the 

 Straits of Bab-el-Mande'b due to more water being forced 

 through the strait on the surface by the persistent S.E. 

 wind of winter than could be evaporated in the closed Red. 

 Sea. 



