( 571 ) 



The tidal curve shows not only at different depths, but also 

 in the older and newer observations, generally the same shape. 

 Its size, on the other hand, both in the older and more recent 

 observations, appears to be smaller near the bottom than near the 

 surface. Also its orientation and the situation of the point in it, 

 which relates to the moment of the moon's transit, or, more generally, 

 the phase of the tidal current, seems to change in a definite sense 

 as the depth increases. This last relation may be specially illustrated 

 by the following table. 



It appears from the table, that the tide is on the whole accelerated 

 in the depth, compared with higher layers; but the table also proves 

 that the phenomenon underlies varying influences, besides constant 

 causes, among which perhaps may be reckonned the shape of the 

 bottom of the sea and ihe rotation of the earth. 



The residual current is by no means constant; at the new obser- 

 vations it has been much stronger than at the old; it shows consid- 

 erable fluctuations also, when the progressive diagrams of the different 

 days of observation are compared. At the new observations this 

 residual current was on an average stronger near the surface than 

 in deeper layers. This particular may perhaps be principally attributed 

 to the action of persisting winds, which at least on the observations of 

 August 1905 and May 1906 had a very marked influence, rendered 

 quite obvious by the special diagrams for these dates. 



The figures for the residual current as deduced from the newer 

 observations are the following: 



These results are worth comparing with the following table of 

 values for the year-average of the residual current at the Noord- 

 Hinder (Lat. 51 G 35'.5N., Long. 2 C 37 / E.), calculated by van dek Stok ') 

 from current-estimations near the surface during five consecutive years. 



x ) Average of depths of 1, 4, 5, 6, 10 M. ; at a depth of 35 M. measurements 

 were made by Van Roosendaal only in February 1905. 



~) J. P. van der Stok, Etudes des Phénomènes de Marée sur les cötes néer- 

 landaises; Kon. Ned. Met. Inst. No. 90, II. p. 67, 1905. 



