( 461 ) 
ground on which the five sluices were built with regard to the 
mean level of the Northsea. The uncertainty of this result mav 
be expressed by a mean error of ±2 cm. 
If we accept this result, we must also assume that the A.P. at 
the tidal station has fallen about 80 mm. from 1700 to 1860, but 
the cause of such a fall is' obvious. 
The mark had namely been made on a gauging rod, which was 
thrust into the water through a hole in the floor of the tidal station 
built over the Y, so far till the cleat at the side of the rod caught 
on the upper side of this floor. In this position the mark on the rod 
indicated the A.P., and the level of the water was determined by 
reading how far above or below the mark the rod was wetted. 
It is clear that as well sinking of the floor of the wooden building 
which rests on poles, as changes of the gauging rod, of the cleat or 
the mark, which are sure to have occurred in these 160 years, 
must change the position of the A.P. at the tidal station; and it is 
certainly less probable that all through* this period the assumed A.P. 
remained unchanged, than that it changed about 8 cm. The impro¬ 
bability that the A.P. at the tidal station should have fallen can, 
therefore, hardly be adduced as refutation of the above result. 
2. Observations with the water gauges along the seashore. 
Mr. Ramaer, Head-engineer, Director of the hydrographic survey 
published an important paper in the transactions of the Royal Institute 
of Engineers in 1908, in which he states the results of an examination 
of the readings of the water gauges for the determination of changes 
m the relative level of the coast and the Northsea. 
His paper owes its importance among others to the circumstance 
that these gauges are under the supervision of Mr. Ramaer, who is, 
t erefore, the most competent judge of their reliability. With regard 
to the reliability I shall, therefore, be entirely guided in my consi¬ 
derations by Mr. Ramaer. 
Mr. Ramaer’s first calculations are based on readings of 8 gauges 
P aced along the coast, which are evidently considered by him as more 
^ourate than the readings of the other gauges. At least he writes: 
e may accept the results found with confidence. This is not the 
Case with Hie other gauges of table IV (probably table V).” The 
series of observations used by Mr. Ramaer begins with 1872, because 
, r0m ^is year most of these gauges have been regularly observed : 
11 ^ds in 1906. 
re ^ r * Hamaer supposes the 35 mean yearly sea-levels, which I have 
Piesented in their true mutual heights in the adjoined figure, to 
