Sept. 7, 1876] 



NA TURE 



413 



energy of Maury, aided originally by the liberal support of his 

 Government, for placing before us in the two-fold interests of 

 science and commerce an abundant store of observed facts in 

 this field ; accompanied, too, by those broad generalisations, 

 which, written with a ready pen and the fervour of an enthusiast 

 gifted with a poetic temperament, have charmed so many readers, 

 and in their practical bearings have undoubtedly advanced navi- 

 gation in practice. 



In our admiration, however, of modern progress we must not 

 in justice pass by without recognition the labours of earlier 

 workers in the same field. So early as the middle of the seven- 

 teenth century we find in Holland, Barnard Vanerius describing 

 with commendable accuracy the direction of the greater currents 

 of the Atlantic Ocean and their dependence on prevailing winds ; 

 the unequal saltness of the sea, the diversity of temperature as 

 the causes of the direction of the winds, and also speculating on 

 the depths of the sea. Vanerius's geographical writings were 

 highly appreciated by Newton, and editions were prepared at 

 Cambridge under the supervision of that great man in 1672 

 and i68i. 



To Dampier the seaman, and Halley the philosopher, we owe 

 graphic descriptions of the trade winds as derived from personal 

 experience ; while the investigations by Hadley of their causes, 

 and the conclusions he arrived at, that they were due to the com- 

 bined effects of the diurnal revolution of the earth on its axis, 

 and the unequal distribution of heat over different parts of the 

 earth's surface, in substance still remairt unchallenged. 



To Rennell we owe a masterly investigation of the currents of 

 the Atlantic Ocean, an investigation, which for precision and a 

 thorough conception of the conditions affecting the subject will 

 long serve as a model for imitation. His period covered some 

 thirty or forty years during the end of the last and the begin- 

 ning of the present century. At that epoch, chronometers — 

 though very efficient — had scarcely passed the stage of trial, but 

 had nevertheless commended themselves to the first navigators 

 of the day, whose aim it was to narrowly watch and test this, 

 to them, marvellous acquisition. Rennell thus commanded 

 nautical observations of a high order of merit ; these he indi- 

 vidually verified, both for determining the ship's position abso- 

 lutely and relatively to the course pursued; and our knowledge 

 of surface-currents was established on the secure basis of diffsr- 

 ential results obtained at short intervals, such as a day or parts 

 of a day, instead of the previous rude estimation from a ship's 

 reckoning extending over a whole voyage, or its greater part. 



At a later date we have by Redfield, Reed, Thom, and others, 

 solidly practical investigations of the gyratory and at the same 

 time bodily progressive movements of those fierce and violent 

 stoims which, generated in tropical zones, traverse extensive 

 districts of the ocean, not unfrequently devastating the narrow 

 belt of land comprised in their track ; and on the sea baffling all 

 the care and skill of the seaman to preserve his ship scathless ; 

 while the clear and elegant exposition by Dove of their law and 

 its application as one common general principle to the ordinary 

 movements of the atmosphere must commend itself as one of 

 the achievements of modern science. 



' While for the moment in the aerial regions, we must not forget 

 the industry and scientific penetration of the present excellent 

 secretary of the Scottish Meteorological Society. His more 

 recent development of the several areas of barometric pressure, 

 both oceanic and continental, bids fair to amend and enlarge our 

 conceptions of the circulation of both the aei-ial and liquid 

 coverings of our planet. 



Looking then from our immediate stand-point on the ex- 

 tent of our knowledge, as confirmed by observational facts of 

 the several branches of physics pertaining to the geography of 

 the sea, just rapidly reviewed, we find that, resulting from the 

 methodical gathering up of " ocean statistics" by our own and 

 other maritime nations, in the manner shadowed forth by Maury 

 and stamped by the Brussels Conference of 1853, we are in pos- 

 session of a goodly array of broad but nevertheless sound results. 

 The average seasonal limits of the trade winds and monsoons, 

 with the areas traversed by circular storms are known ; also the 

 general linear direction and varying rates of motion of the several 

 ocean currents and streams ; together with the diffused values 

 of air and sea surface temperatures, the areas of uniform baro- 

 metric pressure, and the prevalent winds, over the navigable 

 parts of the globe. 



Thus far the practical advantages that have accrued to the art 

 of navigation — and so directly aiding commerce — by the gradual 

 diffusion of this knowledge through the medium of graphical 

 rendering on charts, and concise textual descriptions, cannot be 



over-rated ; still much is wanting in fulnesi ind precision of de- 

 tail, especially in those distant but limited regions more recently 

 opened out by expanding trade. Science views, too, with 

 increasing interest these advances in our knowledge of ocean 

 physics, as bearing materially on the grand economy of nature : 

 essays brilliant and almost exhaustive on some of its subjects, 

 have been given to us by eminent men of our own day ; but here 

 one is reminded, by the diversity in the rendering of facts, how 

 much remains to be done in their correlation, and what an ex- 

 tensive and still expanding field is before us. 



The dawning efforts of science to pass beyond the immediate 

 practical requirements of the navigator are worthy of note. We 

 find — from an admirable paper on the " Temperatures of the Sea 

 at different Depths," by Mr. Prestv/ich, just published in the 

 Philosophical Transactions — that in the middle of last century 

 the subject of deep-sea temperatures first began to attract atten- 

 tion, and thermometers for the purpose were devised ; but it was 

 not till the early part of the present century that the curiosity 

 of seamen appears to have been generally awakened to know 

 more of the ocean than could be gleaned on its surface. John 

 Ross, when in the Arctic seas in 1818, caught glimpses of 

 animal life at the depth of 6,000 feet ; other navigators suc- 

 ceeded in obtaining the temperature of successive layers of water 

 to depths exceeding 6,000 feet, but, so far as I can ascertain, 

 James Ross was, in 1840, the first to record beyond doubt that 

 bottom had been reached, "deeper than did ever plummet 

 sound," at 16,060 feet, westward of the Cape of Good Hope. 



The impetus to deep sea exploration was, however, given by 

 the demand for electric telegraphic communication between 

 countries severed by the ocean, or by impracticable land routes, 

 and the past twenty years marks its steady growth. Appliances 

 for reaching the bottom with celerity, for bringing up its water, 

 for bringing up its formation, for registering its thermal condi- 

 tion in situ, have steadily improved, and thus the several oceans 

 were examined both over present and prospective telegraph 

 routes. Science, aroused by the consideration that vast fields 

 for biological research were opening up — as proved by the re- 

 turns, prolific with living and dead animal matter, rendered by 

 the comparatively puny appliances originally used for bringing 

 up the sea bottom — invoked, as beyond the reach of private 

 enterprise, the aid of Government. Wisely, earnestly, and 

 munificently was the appeal responded to, and thus the 

 Challenger Expedition has become the culminating effort of our 

 own day. 



We have now reached, in all probability, a new starting-point 

 in reference to many of our conceptions of the physics of the 

 globe, and our own special branch may not be the least affected. 

 There is opened up to us, for example, as fair a general know- 

 ledge of the depression of the bed of large oceanic areas below 

 the sea level, as of the elevation of the lands of adjacent conti- 

 nents above that universal zero line. We learn for the first time 

 by the Challenger's results — ably supplemented as they have 

 recently been by the action of the U.S. Government in the 

 Pacific, and by an admirable series of soundings made in the 

 exploratory German ship of war Gazelle — that the unbroken 

 range of ocean in the southern hemisphere is much shallosver 

 than the northern seas, that it has no features approaching in 

 character those grand abyssal depths of 27,000 and 23,500 feet 

 found respectively in the North Pacific and North Atlantic Oceans, 

 as the greatest reliable depths recorded do not exceed 17,000 or 

 17,500 feet. 



The general surface of the sea bed presents in general to the 

 eye, when graphically rendered on charts by contour lines of 

 equal soundings, extensive plateaux varied with the gentlest of 

 undulations. There is diversity of feature in the western Pacific 

 Ocean, where, in the large area occupied by the many groups of 

 coral islands, their intervening seas are cut up into deep basins 

 or hollows, some 15,000, some 20,000 feet deep. In the 

 Northern Oceans one is struck with the fact that the profounder 

 depths in the Pacific occupy a relative place in that ocean with 

 those found in the Atlantic ; both abyssal areas have this, too, 

 in common, the maximum depths are near the land, the sea sur- 

 face temperature has the maximum degree of heat in either ocean, 

 and two of the most remarkable ocean streams — Florida Gulf 

 and Japan — partially encompass them. 



In the Atlantic Ocean, from a high Southern latitude, a broad 

 channel with not less than some 12,000 to 15,000 feet can be 

 traced, as extending nearly to the entrance of Davis Strait : a 

 dividing undulating ridge of far less depression, on which stand 

 the islands of Tristan d'Acunha, St. Helena, and Ascension, 

 separates this which may be named the Western Channel from a 



