( 467 ) 
The rise of the sea-level per century has been derived from the years: 
a. 1855—1860 and 1903—1908 (12 years).196 mm. 
b. 1861—1902 (42 years). 92 » 
c. 1855—1865 and 1898-1908 (22 years).196 „ 
d. j 866—1897 (32 years). 17 » 
e. 1855—1908 (54 years). 193 » 
Now the values a and c are certainly too high, because the years 
1855-1865 were low years, and the years 1898—1906 high years. 
The value d is certainly too small, because the years 1866—1869 
were high years and the years 1885—1897 low years. 
For the assumptions that the rise of the sea-level per century is 
92 and 133 mm., we adjoin a list containing the deviations on 
those assumptions. The mean height of half-tide on Januay 1 st 1882 
(the middle of the period) is in the first case 94 mm. — N. A. P ), 
derived from 42 years; in the second 96,4 mm. -f N. A. P., derived 
from 54 years. (The height of high water and of low water of every 
year only being given in cm., a difference of 5 mm. for every year 
is possible). 
It appears from this list that the direction of the deviation for 
every year is the same in the two assumptions. So this cannot 
decide in favour of one or the other of the assumptions. It further 
appears that the periods of permanent deviation either in positive or 
negative sense may be pretty long, and that the greatest deviations 
are distributed very irregularly. The most probable assumption is that 
for so far as displacement of the zero of the gauges has not exercised 
any influence, the rise lies between 92 and 133 mm. per century. 
Breskens; given the years 1862—1908. 
The rise of the sea-level per century derived from the 47 years 
In the above-mentioned list the deviation on this assumption 
has been given. The mean height of half-tide on July 1 th 1885 
(middle of the period) is 112.6 mm 4- N.A.P. On the whole the 
deviations agree pretty well with those at Muiden. 
In virtue of the above and because the observations at Muiden 
and at Breskens are in fairly good harmony with those of other 
tide-gauges, we may assume as probable that the rise of the sea- 
level in the last 50 years amounts to about 100 mm. per century. 
The Hague, October 1909. H - B - DE Bruijn ’ 
l ) N. A. P. = Amsterdam 
