August i6, 1894] 



NA TURE 



It was my good fortune to be ordered in 1S72 to undertake a 

 series of experiments of the currents and under-currents of the 

 Dardanelles and Bosporus. They proved most interesting. 



It was well known that a surface stream is almost con- 

 tinuously passing out of the Black Sea through the Bosporus 

 into the Sea of Marmara, and again through the Dardanelles 

 into the Mediterranean. Certain physicists, of whom Dr. W. 

 Carpenter was one, were, however, of opinion that a return 

 current would be found under the surface nmning in the 

 opposite direction, and this I was enabled to demonstrate. 



Though from the imperfection of our apparatus, which we 

 had to devise on the spot, we were unable to exactly pro- 

 portionate the quantities of water moving in the two directions, 

 we found, whenever the surface current was rushing south- 

 westward through these straits, that for a certain distance, from 

 the bottom upwards, the water was in rapid motion in the 

 opposite direction. It was an astonishing sight to behold the 

 buoys which supported a wooden framework of 36 square feet 

 area, lowered to depths from 100 to 240 feel tearing up the 

 straits against a strong surface current of as much as three and 

 four miles an hour. It was as perfect an ocular demonstration 

 of a counter under-current as could be wished, and the Turks, 

 who watched our proceedings with much suspicion, were 

 strongly of opinion that the devil had a hand in it, and only 

 the exhibition of the Sultan's lirman saved us from interruption. 

 In the investigation of these currents we found, as u»ual, that 

 the wind was the most potent agent. Though the surface 

 water from the Black Sea is almost fresh, and the bottom 

 water of the heavy Mediterranean density of i'027, it was 

 found that when calm had prevailed the surface current 

 slackened, and at times became nil, whilst the under-current 

 responded by a similar slackening. 



The ordinary condition of wind in the regions of the Black 

 Sea and Sea of Marmara is that of a prevalent north-east wind. 

 This causes a heaping up of the water on the south-west shores 

 of those seas, precisely where the straits open, and the surface 

 water therefore rapidly escapes. 



These straits no doubt present abnormal characters, but, so 

 far as surface currents are concerned, the long series of 

 observations then made convinced me of the inadequacy of 

 diflTerences of specific gravity, which were here at a maximum, 

 to cause any perceptible horizontal flow of water. 



I have said that we were unable to define by direct observa- 

 tion the exact position of the dividing line between the 

 opposing currents, but the rapid change in the specific gravity 

 at a certain depth, which varied on different days, gave a 

 strong indication that the currents changed at this point. 



A Russian officer, Captain Makaroff, afterwards made 

 similar experiments in the Bosporis, but with more perfect 

 appliances, and he found that at the point where the specific 

 gravity changed the currents also changed. 



I have been anxious to obtain similar observations at 

 the Straits of Babel M.indeb, the southern outlet of the Red 

 Sea, where somewhat similar conditions prevail. Here the 

 winds are governed by the monsoons. For half the year the 

 wind blows from the north down the whole length of the sea, 

 causing a surface flow outwards into the Gulf of Aden, and a 

 general lowering of the whole level of the sea of about two 

 feet. P"or the other half of the year the wind at the southern 

 end of the sea is strong from the south-east, causing a surface 

 set into the Red .Sea, over which the general level of the water 

 rises, while the northerly wind continues to blow throughout 

 the northern half. 



At either of these limes I think it is highly probable that 

 there is an under-current in the opposite direction to that at the 

 surface, but unfortunately the sea disturbance is great and 

 observations are very diflicult. 



Observations were, however, made by Captain W. U. Moore 

 in H.M..S. Penguin in 1S90, but at a time when the change of 

 monsoon was taking place. 



The result was peculiar, for it appeared that at a depth of 

 about 360 feet the movement of the water was tidal, while the 

 surface water was moving slowly in one direction — a result 

 generally similar to that obtained by the Americans in the West 

 Indies — but the direction of the tidal flow was directly opposite 

 to what might have been expected, viz. the water ran in while 

 the tide fell, and vice versa. 



More observations are, however, needed here before any 

 certain conclusions can be formed. 



The depth of the ocean is the next great feature which 

 demands attention. 



NO. 1294, VOL. 50] 



On this our knowledge is steadily, though slowly, iucreasiiig. 



The whole of it has been gained during the last fifty year.s. 



Commenced by Sir James Ross, whose means were very 

 small, bat who nevertheless demonstrated that the so-called 

 unfathomable ocean was certainly fathomable everywhere, the 

 sounding of the ocean has continuously proceeded. The needs 

 of submarine cables have constantly demanded knowledge in 

 this particular, and the different cable companies have had a 

 large share in ascertaining the facts. 



Expeditions, whose main object has been to obtain soundings, 

 have been sent out. Great Britain and the United States taking 

 the first place ; but most maritime nations have aided. 



In the immediate past the additions have mainly been from 

 the soundings which II. M. surveying ships continually take 

 whenever on passage from one place to another, from the work 

 of our cable companies, and from United States vessels. 



We have, as a result, a very fair general knowledge of the 

 prevailing depths in the Atlantic, but of the Indian and Pacific 

 Oceans it is very fragmentary. We have enough to give us a 

 general idea, but our requirements increase as years roll on. 

 It is a vast task, and, it may be safely said, will never be com- 

 pleted ; for we shall never be satisfied until we know the 

 variations of level under the water as well as we know those on 

 the dry land. 



It is hopeless to do more than to briefly sketch the amount 

 of our knowledge. 



First, as to the greatest depths known. It is very remark- 

 able, and from a geological point of view significant, that the 

 very deepest parts of the ocean are not in or near their centres, 

 but in all cases are very near land. 



One hundred and ten miles outside the Kurile Islands, which 

 stretch from the northern point of Japan to the north-east, the 

 deepest sounding has been obtained of 4655 fathoms, or 

 27,930 feet. This appears to be in a deep depression, which 

 runs parallel to the Kurile Islands and Japan ; but its extent is 

 unknown, and may be very large. 



Seventy miles north of Porto Rico, in the West Indies, is 

 the next deepest cast known, viz. 4561 fathoms, or 27,366 

 feet ; not far inferior to the Pacific depth, but here the deep 

 area must be comparatively small, as shallower soundings have 

 been made at distances sixty miles north and east of it. 



A similar depression has been sounded during the last few 

 years west of the great range of the Andes, at a distance of 

 fifty miles from the coast of Peru, where the greatest depth 

 is 4175 fathoms. 



Other isolated depths of over 4000 fathoms have been 

 sounded in the Pacific. One between the Tonga or Friendly 

 Islands of 4500 fathoms, one of 4478 fathoms near the 

 Ladrones, and another of 442S fathoms near Pylstaart Island, 

 all in the Western Pacific. They all require further investiga- 

 tion to determine their extent. 



With these few exceptions, the depth of the oceans, so far 

 as yet known, nowhere comes up to 4000 fathoms, or four sea 

 miles ; but there can be little doubt that other similar hollows 

 are yet to be found. 



The sea with the greatest mean depth appears to be the vast 

 Pacific, which covers 67 millions of the 1S8 millions of square 

 miles composing the earth's surface. 



Of these 188 millions, 137 millions are sea, so that the Pacific 

 comprises just one-half of the water of the globe, and more 

 than one-third of its whole area. 



The Northern P.icific has been estimated by Mr. John 

 Murray to have a mean depth of over 2500 fathom*, while the 

 Southern Pacific is credited with a little under 2400 fathoms. 

 These figures are based on a number of soundings which 

 cannot be designated otherwise than very sparse. 



To give an idea of what remains to be done, I will mention 

 that in the eastern part of the Central Pacific there is an area 

 of 10,500,000 square miles in which there are only seven sound- 

 ings, whilst in a long strip crossing the whole North Pacific, 

 which has an area of 2,800,000 square miles, there is no sound- 

 ing at all. Nevertheless, while the approximate mean depth 

 I am mentioning m.iy be considerably altered as knowledge 

 increases, we know enough to say that the Pacific is generally 

 deeper than the other oceans. "The immensity, both in bulk 

 and area, of this great mass of water, is difficult to realise ; but 

 it may assist us when we realise that the whole of the land on 

 the globe above water level, if shovelled into the Pacific, would 

 only fill one-seventh of it. 



The Indian Ocean, with an area of 25,000,000 square miles, 

 has a mean depth, according to Mr. Murray, of a little over 



