348 THE PHYSICAL CONDITION OF THE OCEAN. 



far as surface currents are concerned, the long series of observations 

 then made convinced me of tlie inadequacy of difterences of si^ecilic 

 gravity, which were here at a maximum, to cause any perceptible hori- 

 zontal 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 tbe rapid change in the specific gravity at a cer- 

 tain deptb, which varied on different days, gave a strong indication 

 that the currents changed at this point. 



A Russian officer, Ca]itain Maknroflf, afterwards made similar experi- 

 ments in the Bosporus, but with more perfect ap])linnces, 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 Mandeb, the southern outlet of the Red Sea, where somewhat 

 similar conditions prevail. Ilere the winds are governed by the mon- 

 soons. For half the year the wind blows from the north down the 

 whole length of the sea, causing a surface flow outward into the Gulf 

 of Aden and a general lowering of the whole level of the sea of about 

 2 feet. For the other half of the year the wind at the southern end of 

 the sea is strong from the southeast, 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 times I think it is highly probable that there is an undercurrent in 

 the opi)osite direction to that at the surface, but unfortunately the sea 

 disturbance is great and observations are very difficult. Observations 

 were, however, made by Capt. W. U. Moore in H. M. S. Pou/uin in 

 1890, 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 Avhat might have been expected, 

 viz, the water ran in while the tide fell, and vice versa. More obser- 

 vations are, however, needed here before any certain conclusions can 

 be formed. 



The depth of tlie ocean is the next great feature which demands 

 attention. On this our knowledge is steadily, though slowly, increas- 

 ing. The whole of it has been gained during the last fifty years. Com- 

 menced by Sir James Ross, whose means were very small, but who 

 nevertheless demonstrated that the so-called unfathomable ocean was 

 certainly fathomable everywhere, the sounding of the ocean has con- 

 tinuously proceeded. The needs of submarine cables have constantly 

 demanded knowledge in this i)articular, and the different cable compa- 

 nies have had a large share in ascertaining the fixcts. 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 



