CRUISES OF THE "MICHAEL SARS " 67 



is accordingly of the utmost importance, not merely because 

 of the light it throws on the question of ocean circulation, but 

 also because of its value to navigation. As early as 1871 Nares 

 and Carpenter made a study of these currents, and important 

 investigations have been made in later days by the Danish 

 research vessel "Thor" under the direction of Joh. Schmidt. 

 No direct measurements of the actual velocities of the currents 

 at different depths and their direction had previously been 

 undertaken, but current-meters, especially the excellent one 

 constructed by V. W. Ekman, put it in our power to make the 

 attempt. 



The " Michael Sars " had previously measured currents off 

 the coast of Norway by anchoring a life-boat fore and aft with 

 grapnels and a stout hemp line. We endeavoured to work on 

 the same principle in the Strait of Gibraltar (Station 18), but 

 were unsuccessful at first ; one line after the other parted, owing 

 to the velocity of the current. Finally we had to anchor the 

 ship itself with i|^-inch steel line and a warp anchor, in 400 

 metres of water on a hard bottom. This held, and she lay at 

 anchor from 1.30 a.m. till 5 p.m. on the 30th April. During 

 this time Helland-Hansen worked unceasingly. One current- 

 meter was used continuously at a depth of 10 metres, and 

 another was lowered to different depths right down to the 

 bottom. In addition he took a series of water-samples and 

 temperatures at different depths. 



He found that there were two strong currents in the Strait, 

 one going east from the Atlantic into the Mediterranean in the 

 upper layers, and one going west at the greater depths. The 

 limit between them was for the most part at a depth of about 

 150 metres, but it varied so much that in the afternoon between 

 2 and 2.30 P.M. it was at a depth of 50 metres, while between 

 4 and 5 A.M. even at the very surface the current went westwards. 

 These variations practically coincided with the tidal movements. 



There were high velocities in the upper east-going current ; 

 at 10 metres the velocity varied between i and 2^ knots, and 

 at 25-30 metres between 1.7 and 3 knots. At a depth of 

 100-120 metres the current was always westerly, but the 

 velocity was only between half a knot and a knot, whereas at 

 150-200 metres, where the current was also westerly, the 

 velocity varied from 0.3 knot to as much as 5 knots; close to 

 the bottom a velocity of ^ knot was measured. Helland- 

 Hansen's interesting observations are the first reliable figures 

 regarding the niovements at the different depths, and they are 



