( 706 ) 



As ineaii level of tlie Y before Amslenlaiii willi r('jj!;ai'(l lo ilie 

 zero adopted in tlie (idal slalioii (zero of AinslordaiM) we shall assuiue 

 the half sum of the high and low water. 



For the same 58 years we derive for that mean the following values. 



TABLE 11. 



These values show thai llx^ nieau .sea le\ el has not remained 

 unehanged with regard lo I he adopted /.ero of Amsterdam. This 

 becomes still more evident if we form the meaus of the 3 periods 

 of 18 years. We then obtain: 



1708,5 —160,3 mm. ± 5,9 mm. 



