42 REPORT— 1873. 



Carpenter's theoretical conclusion that a strong undercurrent must exist between 

 the ^gean and the Black Sea. 



Although it is commonly supposed that the Dardanelles and the Bosphorus 

 s««r/rtce-currents are overjlow-cuxienta, carrying ofl' the excess of fresh water dis- 

 charged by rivers into the Black Sea, yet it is now clear that they are in great 

 measiu'e tcind-cuxients. During about three quarters of the year the wind blows 

 pretty steadily fi'om the N.E. (that is, down the Straits) ; and, as a rule, the stronger 

 and more continuous the wind, the stronger is the surface out-current. On calm 

 days, the out-cm'rent of the Dardanelles is usually slack ; and if, as sometimes 

 happens, a strong wind blows from the S.W., its ilow may be entirely checked. 

 It requires a continuance of strong S.W. wind, however, to reverse its direction; 

 and its rate, when reversed, is never equal to that of tlie out-current. The speed 

 of the Dardanelles cun-ent varies at different parts of the Strait, according to its 

 breadth — being usually about one knot per hour at Gallipoli, and three knots in the 

 " Narrows '' at Chanak Kaleksi, where, with a strong N.E. wind, it is sometimes as 

 much as four and a half knots, the average of the whole being estimated by Oapt. 

 Wharton at one and a half knots. — The Bosphorus current has not been as care- 

 fully studied as that of the Dardanelles ; but Capt. Wharton states that its rate is 

 greater, averaging about two and a half knots per houi', apparently in consequence 

 of the limitation of its channel, which is scarcely wider at any point than is the 

 Dardanelles at the "Narrows." It continues to run, though at a reduced rate, 

 when there is no wind ; and it is onlj' in winter^ after a continued S.W. gale of 

 long duration, that a reversal of the Bosphorus current ever takes place. 



It might have been supposed that, as the greatest depth of these two Straits 

 does not exceed fifty fathoms, the determination of the question as to the existence 

 of an undercm-rent would be a comparatively easy matter. But it is rendered 

 difficidt by the very rapidity of the movement, alike in the upper and the lower 

 stratum ; and the results of the earlier experiments made by Capt. Wharton, in 

 which he used the cm-rent-drags that had been found to work satisfactorily in the 

 Strait of Gibraltar, were not conclusive. But perceiving from the very oblique 

 direction of the suspending line, that the undercurrent must be acting on the 

 current-drag at a great disadvantage, Capt. Wharton set himself to devise a drag 

 which should hang vertically, even when the suspending line was oblique, so as to 

 expose a large surface to the impact of a current at right angles to it. This worked 

 satisfactorily, and gave the most conclusive evidence of the existence of a powerful 

 undercurrent, by dragging the suspending buoy iinvards against the sui-face-cur- 

 rent ; the force of which, aided by wind, was sufficient on several occasions to 

 prevent the row-boats from following the buoy, only the steam cutter being able 

 to keep up with it. The following, which is the most striking of all his results, 

 was obtained in the Bosphorus on the 21st of last August, with a surface-current 

 running outwards at the rate of three and a half knots per horn-, and a N.E. wind 

 of force 4. " When the current-drag was lowered to a depth afterwards assumed 

 to be twenty fathoms, it at once rushed violently away against the sm-face-stream, 

 the large buoy and a small one being pulled completely xmder water, the third alone 

 remaining visible. It was a wonderful sight to see this series of floats tearing 

 through the water to windward. The steam cutter had to go full speed to keep 

 pace with it." It is obvious that the real rate of the undercurrent must be very 

 much greater than that indicated by the actual movement of the float, since the 

 current-drag impelled by it had to draw the large suspending buoys and the upper 

 part of the line against the powerful surface-current running at three and a lialf 

 knots an hour in the opposite direction, tlieir motion through the water therefore 

 being nearly four and a half knots an hour. 



The difference in the specific gravity of water obtained from different depths was 

 usually found in Capt. Wharton's investigations (as in the author'sj to afford, imder 

 ordinary circumstances, a very sure indication of the direction of the move- 

 ment of each stratum ; the heavy water of the iEgean ffowing ?V(wards, and the 

 light water of the Black Sea 02</wards. And it was indicated alike by both modes 

 of inquiry, that the two strata move in opposite directions, one over the other, 

 with very little intermixture or retardation, the passage from the one to the other 

 being usually very abrupt. In a few instances there was a departure from the 



