1873.] 



of the Dardanelles and Bosphorus . 



391 



The boat on the Asiatic side obtained another undercurrent of and 

 ■fy at 17 and 23 fathoms, but at 34 fathoms it again drifted slowly to lee- 

 ward. Surface-current about 3 knots. 



The countercurrents obtained here were at less depths than any before 

 observed. 



October 1st. Four boats together, across the western entrance to the 

 Dardanelles from Koum Kaleh to Seddul Bahr. The wind was light 

 and variable, but it had been blowing half a gale from the N.E. the three 

 preceding days, and the surface-stream was strong, nearly 3 knots, but 

 with smooth water. The results this day were curious, as instead of the 

 under countercurrent existing from the bottom upwards to about 

 15 fathoms, as usual, it was found between 10 and 20 fathoms, running 

 strongest at 15 ; but below 20 fathoms the water was apparently moving 

 in the same direction as the surface. 



Here, too, at the surface is no longer the pure sea of Marmara water ; 

 the density shows it to be mixed with the Mediterranean, probably from 

 a counter surface-current that sometimes runs up inshore on the 

 European side. 



Bosphorus. 



The general now of the water is from the Black Sea to the Marmara, 

 and at an average rate of about 2 \ knots ; but the speed of the current 

 will vary from hour to hour, and the course of the strait is so tortuous 

 that the water runs in swirls and streams of different speeds. 



Generally the current runs quicker in the afternoon than the forenoon ; 

 and as the mornings are usually calm and the N.E. breeze gains strength 

 during the day, this seems to be attributable to that fact. 



The remark made with regard to the Dardanelles currents, that, " as 

 a rule, in a calm the currents are slack," does not, however, apply to the 

 Bosphorus. 



On two occasions during the * Shearwater's ' visits the current seemed 

 to have ceased altogether, without any apparent cause, calms existing at 

 the time, but in certain places (as the Devil's Current and off Seraglio 

 Point) the water was still draining down. The Turkish fleet which lie 

 in the strength of the current, opposite Scutari, were swung in different 

 directions. 



It is reported that in the winter season, when S.W. gales of long 

 duration are not uncommon, the current will run the opposite way with 

 some strength. 



The current gathers strength as it advances down the strait ; at 

 the northern entrance it was never found so strong as at the southern. 



A general undercurrent running counter to the surface-stream was 

 found at both ends of the Bosphorus ; in the deep channel the rate of 

 this, as recorded by the drift of the buoy, varied from ly 1 ^ to T 2 y- of a 

 knot, and the depth at which it was found varied from 15 to 30 fathoms. 

 This, it must be remembered, is subject to great corrections. 



2 i 2 



