( 567 ) 



The apparatus of Nansen appeared to be unfit for the measure- 

 ments on the North Sea: it was not calculated for the strong tidal 

 currents occurring there (e.g 60 — J(H) cm/sec), and also the putting 

 out of the apparatus in unfavourable weather was hardly possible 

 without doing harm to the instrument. In more quiet water, however, 

 it seems to be very useful. 



The apparatuses of Pettersson and Ekman appeared to be better 

 tit for the observations in the North Sea. Some improvements in the 

 construction were proposed, partly also put into practice, by Van Roo- 

 sendaal and Wind, by which the instruments have gained in fitness. 

 For a description of the construction of the current-meters used, and 

 the experience made in using them, we may refer to the publications 

 mentioned. The following few words may be sufficient here. 



It appeared that pretty large oscillations, e. g. 15° to both sides 

 round the longitudinal axis, did not yet render observation impossible. 

 In 32 out of nearly 200 observations by Van Roosendaal as much 

 as the figure 4 was noted for the motion of the sea, in 40 to 50 

 cases the oscillations amounted to 10 a 20° to either side, and yet 

 the accuracy and certainty of these measurements were only excep- 

 tionally insufficient. 



In the parallel-observations with the apparatus of Pettersson ami 

 Ekman the agreement in indicating the velocity appeared satisfactory'. 

 In one series of 23 measurements e. g. the average difference amounted 

 to 4.8 cm/sec, whilst the smallest was 3.1, the greatest 6.3. 



Nor did the indications of direction, as given by the two instru- 

 ments, show r great differences. The observations with Ekman's appa- 

 ratus bear to some extent a check in themselves, as, by the construction 

 of the instrument, every observation includes a series of consecutive 

 readings at small intervals. In by far the greater part of the reading- 

 observations these separate did not considerably vary. In 128 cases 

 the direction of the current could be estimated from them : 



To less than 10° in 105 cases, 

 10-20 15 



20—30 2 



30—40 



40—50 2 



more than 50° 4. 



Compared with the probable direction, as derived from the instru- 

 ment of Ekman, that which was determined by means of Petterson's 

 instrument deviated : 



