( 709 ) 



tioiis we derive tlic following values for the height of the higher 

 bench mark above the A. P. according to the mean of the 5 sluices 

 in 1860 : 



Stamkart v. D. Sterr mean 



3628 mm. 3624 mm. 3627 mm. 



In the derivation of the mean value we have, with regard to the 

 mean errors, accorded a greater weight to Stamkakt's result. 



h) 1875 onr colleague Dr. Lely by means of a still preciser level- 

 ling under direction of Cohkn Stuart has derived 3622 mm. for 

 the same difference in height. 



The differences between the results of 1860 and those of 1875 

 may be explained very well by errors of observation, so that we 

 may accept with a high degree of accuracy that the bench mark 

 in the St. Anthonicwaag between 1860 and 1875 has not varied 

 with regard to the 5 sluices and that in 1860 the height of the 

 mark above the A. P. of the slnices was 3623 mm. with a mean 

 error of ± 2 mm. 



If from this value we subtract 3705, i. e. the height of the mark 

 above the A. P. in the tidal station found by Dr. Stamkart in 1860 

 we find : 



height of the A. P. according to the mean of the 5 sluices above 

 the A. P. in the tidal station in 1860^:82 mm. 



The mean error of this result is about ± 3 mm. 



As in 1860 the height of the A. P. in the tidal station was elevated 

 80 mm. above the mean level of the Y, it follows that iji 1860 the 

 A. P. deiived from the mean of the 5 sluices above the mean sea 

 level is : 



80 + 82 = 162 mm. ± 13 mm. 



If we compare this value with the corresponding value of the 

 year 1700, i. e. 165, we may conclude that the height of the mean 

 sea level in the Y, and hence the mean level of the Northsea on 

 our coast has not perceptibly varied with regard to the ground 

 in which the foundations of the 5 sluices are built. 



The uncertainty of this conclusion may be expressed by a mean 

 error of ±: 18 mm. 



The 5 sluices are not in close neighbourhood of each other, the 

 extreme ones are separated by a distance of one kilometre; hence it is 

 over a fairly extensive part of the ground on which Amsterdam is built 

 lliat the level of the land with regard to the level of the Northsea 

 has remained unchanged during more than one cejitury and a half. 



With the same degree of probability with which we^ have derived 



