392 On the Currents of the Dardanelles and Bosphorus. [June 19, 



Details of Undercurrent Observations. — Bosphorus. 



The spot chosen for the observations at the southern end of the 

 Bosphorus was between Seraglio Point and Leander's Tower. 



Here the whole surface runs down with great velocity, with no side 

 eddies. There is a narrow deep channel of 34 fathoms close to the 

 Stamboul side, otherwise the depth does not exceed 20 fathoms. In this 

 deep channel the up undercurrent was found. 



On August 21st the drag * was tried in a N.E. wind, force 4, and with 

 a surface-current of 3| knots. When lowered to a depth afterwards 

 assumed to be 20 fathoms, it at once rushed violently away against the 

 surface-stream. 



On the 12th of October the steam cutter tried again in the deep 

 channel. This day was one of those when the surface-currents in the 

 Bosphorus were unaccountably slack and variable. At Therapia, near 

 the north end, the water was motionless, while at Seraglio Point, where 

 the observations were made, the current was only 1| knot. 



The result of the observation was a counter undercurrent of one knot 

 at a depth of 15 fathoms. This makes the surface-current much shallower 

 than the other observations. 



On the 14th October, though calm and smooth, the surface-water was 

 rushing down at three knots an hour ; observations showed an up under- 

 current at 22 fathoms, but no" nearer to the surface, and at that depth 

 only at the rate of a quarter of a knot, but the water is of the Mediter- 

 ranean density a few fathoms higher. 



On the 15th of October the surface-current was very rapid ; 4J knots 

 was recorded off Leander's Tower. The results were nearly identical 

 with the previous days. Up current was obtained in the deep channel. 



The experiments at the north entrance of the Bosphorus were made 

 off Pil Burnu, where the strait is contracted by two opposite points, and 

 where no side eddy exists. 



On the 23rd of August the drag gave in the deep channel, at 40 and 30 

 fathoms, an undercurrent of ly 1 ^- and T \ knot respectively, the surface 

 only running 1 T ^ knot. 



This, during all the observations, seemed to be the invariable rate of 

 the surface-current here, wind seeming to have little effect on it. 



Densities changed between 25 and 30 fathoms. At this point also 

 (26 fathoms) was a curious stratum of cold water of 54°, the water 

 immediately below being 62°, and that above, 60°. The next day corrobo- 

 rated this. 



On the 17th of October, undercurrent was again found at 30 fathoms 

 and below, but not so strong as on August 23rd. The two months' 

 interval had made some difference in the temperatures, but little or none 



* For these observations a wooden drag was employed similar in design to that 

 before described ; it weighed 115 lbs, in air, and required 175 lbs. tg sink it, 



