(193°) 
Thickness of the ice in mm. 
1884 1885 1886 1887 1888 L689... 1890 
January 22 387 201 298 310 204 43 
February 53 34 323 266 360 156 171 
March 6 24 211 110 223 124 93 
November 46 74 6 43 145 27 267 
December 95 58 96 121 51 199 811 
I took for the months in question the four ones in which the ice 
has the greatest thickness, and two other months in which the 
thickness too was great, following immediately on two of the for- 
mer, as we may suppose the ice still existed during that time. The 
selected months are underlined in the table. 
I found that in these months A is too small. It is difficuit to find 
a cause for this, as, excepted at Delfzyl and Statenzyl, there are no 
tide-gauges in the Eems and the Dollard, and the gauge at Statenzyl 
does not work when the tide is low. Probably it is due to the 
ice on the mud-banks of the Dollard. Generally the effect of 
the ice is to raise high-watermark at the mouth of the river, but 
this is not the case at Delfzyl. On the contrary, the range of the 
tide is less in the months with ice. Probably both V and £ are 
increased, but & more than V, and therefore the range is smaller 
and half-tide considerably higher, the mean sea-level is less increased 
than half-tide and hence the difference A is smaller. 
The heights at 2 and 8 o’clock in the months January 1891 and 
February 1895, when there was much ice, give also corresponding 
results. 
- In the foliowing table are given the values A, the corrections and 
the remaining differences, for the 5 months in which A is a maxi- 
mum, the 5 months in which 4 is a minimum, the months with 
ice and two other months in which the error or the remaining diffe- 
rence is greater than 15 mm, 
14* 
