388 



Commander J. L. Wharton on the Currents [June 19, 



As a general rule, the stronger and more continuous the N.E. wind, 

 the stronger the S.W. set ; but the surface-currents are capricious in their 

 rates, the wind seeming to affect them more at some times than at others. 

 This is probably owing to the different winds that may be blowing at the 

 two ends of the straits, it being a common occurrence that a strong S.W. 

 wind exists at the southern end simultaneously with a N.E. one at the 

 northern. This was verified on several occasions, and doubtless checks 

 the flow of water. 



On calm days the current will usually be slack to the S.W. ; but there 

 are exceptions to this also, and it will sometimes even run to the N.E. 

 It may, however, be safely stated that the current is rarely strong when 

 there is no wind. 



The general average rate of the current may be taken at 1| knot 

 from one end of the strait to the other ; but in some places, as at Chanak 

 Kalehsi, it will run 3 knots, when at Grallipoli it is but 1 knot. 



The maximum current is at Chanak, where, with a strong N.E. wind, 

 it will attain a speed of 4| knots. 



As has been stated, a south-westerly wind will stop the current in the 

 upper part of the strait, and a long continuance will cause it to change 

 entirely its direction, but it will never run more than a knot to the north- 

 eastward. 



Though the maximum lunar tide is only 3 or 4 inches, the water some- 

 times rises as much as 2 feet above its usual height, which may be ac- 

 counted for by the same cause — i. e. the different winds at the two ends of 

 the straits checking the flow below, and causing the water to accumulate 

 above. 



The observations for undercurrent have been made, as far as possible, 

 in different kinds of weather, so as to ascertain what influence the wind 

 might have on the movement of the water*. 



If the observed rates and areas on October 4th be taken, it makes the 

 outflow to the inflow as 3 to 1 ; but every correction will diminish this 

 ratio, and it is probably nearer 3 to 2 : or, in other words, the quantity 

 of water flowing from the Marmara is half as much again as that 

 which it receives back from the Mediterranean ; but this is a very 

 vague approximation. 



* After various modifications, the drag finally adopted was a fiat board 6 feet square, 

 •with a wing at right angles to the centre of it 2 feet in length. 



To the extremities of this short wing a sling is made fast, and to this sling the sup- 

 porting line to the buoy is bent at such a point as will keep the surface of the drag 

 vertical when the strain comes on. 



It weighs 70 lbs. in air, and took 120 lbs. of lead to sink it satisfactorily. 



The line was ordinary lead line. The float was an iron nun buoy, 5 feet long by 1 in 

 diameter in the centre, capable of supporting 80 lbs. 



The pulling boats used drags of a similar shape, 4 feet square, of canvas, laced to a 

 wooden frame to prevent collapsing, which did not require such heavy weights to sink 

 them. 



