702 REPORT — 1894. 



not in tlie trade wind areas, but are the result of these drifts meeting one another 

 and being compressed by the conformation of the land. We cannot, therefore, 

 expect this theoretical effect to be realised. 



One instance of the underrunning of one current by another is brought very 

 plainly to our notice in the North Atlantic, to the east of the Great Bank of 

 Newfoundland, where the icebergs borne by the arctic current from Baffin Bay 

 pursue their course to the southward across the Gulf Stream running eastward. 



These great masses of ice, floating with seven-eighths of their volume under the 

 surface, draw so much water that they are all but wholly influenced by the under- 

 current. A large berg will have its bottom as much as six or seven hundred feet 

 below the surface. The only reason that these bergs continue their journey south- 

 ward is the action of the cold under-current. 



It was my good fortune to be ordered in 1872 to undertake a series of experi- 

 ments of the currents and iinder-currents of the Dardanelles and Bosporus. They 

 proved most interesting. 



It was well known that a surface stream is almost continuously passing out of 

 the Black Sea through the Bosporus into the Sea of Marmara, and again through 

 the Dardanelles into the INlediterranean. Certain physicists, of whom Dr. W. 

 Carpenter was one, were, however, of opinion that a return current would be found 

 under the surface running 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 proportionate 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 1 00 to 240 feet, 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 

 denion.stration of a counter imder-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 firman saved us from 

 interruption. In the investigation of these currents we found, as usual, 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 1'027, 

 it was found tbat when calm had prevailed the surface current slackened, and at 

 times became nil, whilst the imder-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 N.E. 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 differences of specific gravity, which were here at a maximum, to 

 cau«e any perceptible horizontal flow of water. 



I have said that we were unable to define by direct observation 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 diflerent days, gave a 

 strong indication that the currents changed at this point. 



A Russian officer, Captain Makaroff", afterwards made similar expei'iments in 

 t^ie Bosporus, but witii more perfect appliances, and he found that at the point 

 where the specific gravity changed the currents also changed. 



J have been anxious to obtain similar observations at the Straits of Bab-el- 

 Mand^h, the southern outlet of the Eed 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. For 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, 



