82 



NA TURE 



[May 27, 1897 



///. Value of a. 



High water, Ymuiden, 1895 



1896 



Low water, Ymuiden, 1895 



3 centimetres 



Low water Ymuiden, 1896 

 High water Hoek 



van Holland... 1896 



a ■=■ -1 centimetres 



In calculating the effect of wind and atmospheric pressure on 

 the time of high water at Ymuiden in 1895 ^nd 1896, and at 

 Hoek van Holland in 1896, exactly the same method has been 

 followed. 



The formula by which this effect can be expressed, is the 

 following : — 



a = KR + Rj(B-76-0). 



Cr means the correction in minutes to be applied to the pre- 



dicted time. For the rest the form of the formula is in every 

 way equal to that for the height, except the disappearing of the 

 term a. At absolute calm the mean time of high water, there- 

 fore, will not diff'er from the normal. The sign + signifies that 

 the observed time of high water is later than the predicted, the 

 propagation of the tide being retarded. 



The following tables again give an idea of the results and the 

 obtained degree of exactitude : — 



As an explanation, it may be mentioned that the velocity of I by k — \v^ {k being expressed in kg. per m^) ; and the pressure k 

 wind being v metres per second, the pressure can be represented | being known the velocity v= sl^F. 



NO. 1439. VOL. 56] 



