ATLANT. DEEP-SEA EXPED. 1910. VOL. il PHYSICAL OCEANOGRAPHY AND METEOROLOGY 



111 



and wind, according to their relative strength. Notes on 

 the wind are found on p. 60*. At 2'' 40"" the wind and 

 the current (at 9 metres) had almost the same direction, 

 about 180' different from the heading of the ship. At 

 5'' 30"" the surface current was evidently near its ma.xi- 

 mum (at 9 metres between 30 and 35 cm. sec); the ship 

 then had a position which can easily be explained by the 

 composite action of current and wind. At 11'' 30™ the 

 current was weak and the ship lay directly against the 



of 24 cm. /sec. and a minimum of 19 cm. /sec. according 

 to the analysis above. The maximum occurs 2' 2 hour 

 before and 3V2 hour after the passage of the moon; the 

 direction is then N 16' E or S 16" W. This semi-diurnal 

 tidal current rotates cum sole. 



As at Stat. 18, the N.- and E. -components at Stat. 

 58 show an appreciable average variation during 12 lunar 

 hours as indicated by the broken lines in Fig. 44. Both 

 components show lower values at 21 L. H. than at 9 L. H., 



46 m. 



91m. 



457m. 

 .A- 



ih^ 



.kjO" 



roA 



752m. 



Fig. 46. The currents at various depths at Stat. 58. 



10 ?0 30 



1 1 1 



wind. — The variations in the heading of the ship between 

 9^° and IP" o'clock coincided with comparatively large 

 variations in the observed velocity and direction of the 

 current, the observations having then probably been in- 

 fluenced to a considerable degree by the ships's move- 

 ments. Otherwise the current measurements seem to 

 be fairly reliable. 



Fig. 44 illustrates the variations of the N.- and E. -com- 

 ponents of the current at 9 metres. When the hourly 

 values of the components are used without reduction the 

 harmonic analysis beginning with 9 L. H. (1" 20" L. M. T.) 

 results in the following equations: 



z; zrr - 3-3 + 23-4 cos 30 (H + 3) + 0-5 5//; 30 (H f 3) 

 u= 7-0 -+- \-7 cos 30 (H -i- 3) -^ ]9-7 sin 30 (H + 3) 



This gives a rest-current with a velocity of 8 centi- 

 metres per second towards S 64° E. It is weak compared 

 with the semi-diurnal tidal streams which have a maximum 



the difference being especially great as regards the N. -com- 

 ponent. When we reduce the hourly values for this 

 average variation in the same way as is done for the 

 observations at Stat. 18, we obtain the following results: 



-y = - 3-9 -L 22-3 cos 30 (H + 3) - 3-6 sin 30 (H + 3) 

 11=^ 6-8+ \\ cos30 (H + 3)-\-\7-?,sin30 (H -\-3) 



This means a rest-current of 8 centimetres per second 

 towards S 60° E, /. e. practically the same values as were 

 found by the first analysis. The maximum of the rotatory 

 tidal current amounts to 23 cm./sec. and the minimum to 18 

 cm. /sec. The maximum current appears one hour earlier 

 than the time found above, but the rotation goes in the 

 same direction (cum sole). 



The average variation from 9 to 21 L. H. may be 

 caused by tidal changes with a diurnal period or by changes 

 in air-pressure and wind over a wide area, as was the 

 case in the Straits of Gibraltar. If this variation at Stat. 



