THE PHYSICAL CONDITION OF THE OCEAN. 347 



trade-wind areas, but are the result of these drifts meeting one another 

 and being compressed by the conformation of the land. We can not 

 therefore expect this theoretical effect to be realized. 



One iuvstance of the nnderrunning of one current by another is 

 brought very plainly to our notice in the North Atlantic to the east of 

 the Great Banks of ^STewfoundland, 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 wliolly influenced by the undercur- 

 rent. A large berg will have its bottom as much as 600 or 700 feet 

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

 journey southward is the action of the cold undercurrent. 



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

 of experiments of the currents and undercurrents 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 Mediterranean. 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 w^e had to devise on the spot, we 

 were unable to exactly proj)ortionate the quantities of water moving 

 in the two directions, we found, whenever the surface current was 

 rushing southwestward through these straits, that for a certain dis- 

 tance, from the bottom upward, 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 30 square feet area, lowered 

 to depths from 100 to 210 feet, tearing up the straits against a stroug 

 surface curient of as much as 3 and 1 miles an hour. It was as per- 

 fect an ocular denu)nstratiou of a counter undercurrent as could be 

 wished, and the Turks, who watched our j)roceedings with much sus- 

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

 only the exhibition of the Sultan's flrman 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 that wheu calm had prevailed the surface 

 current slackened, and at times became nil, w^hile the undercurrent 

 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 northeast wind. '1 his causes a 

 heaping up of the water on the southwest shores of those seas, pre- 

 cisely where the straits open, and the surface water therefore rapidly 

 escapes. These straits no doubt present abnormal characters, but, so 



