[15] OYSTER CULTIVATION IN THE NETHERLANDS. 1015 
time. We hardly need say, that the establishment of such stations of 
observation goes beyond the financial means of the Zoological Station. 
Private enterprise should therefore share this burden with us. 
The daily observations, which, as has been mentioned, are taken three 
times a day, are transmitted to us, and entered on specially-prepared 
forms. From these forms it will appear that the observations were not 
only taken at certain regular hours, but also at a uniform depth, which, 
at low water, was still 3 meters under the surface of the water. We 
thought that thereby we should increase the value of these observa- 
tions for drawing comparisons. 
Besides this series of observations, which were in part at least en- 
trusted to subordinates, Mr. van Kervel, during August, took a number 
of observations, with a view to obtaining the greatest possible degree of 
accuracy, by thus controling the observations taken at Tholen, Wemel- 
dinge, &c. These observations were unfortunately somewhat limited by 
the exceedingly unfavorable condition of the weather. We deem itim- 
portant to give the results of these observations in their entirety, as, in 
our opinion, furnishing important hints as to the method to be followed 
in future observations on the Hastern Scheldt.* 
Mr. van Kervel adds the following remarks to this table: 
“Tt is somewhat surprising that out of more than 30 careful observa- 
tions from which the table has been prepared, the difference of tem- 
perature between the bottom and surface water is so small, compared 
with the difference, observable in this respect, in the observations taken 
at Tholen and Wemeldinge.” 
We shall have to ascertain, by further observations, whether these 
differences are caused partly by the presence of a larger quantity of 
marsh water, and partly by the main current of the Hastern Scheldt 
which at Wemeldinge flows close to the bank. 
The figures given in said table furnish ample food for thought; they 
prove that, at the time when these observations were taken by means 
of excellent instruments and with the greatest care, the differences of 
temperature at various points of the Eastern Scheldt, between the bot- 
tom and the surface, were very small and in some cases hardly notice- 
able. 
The water in the deep places and that in the shallow places does not show 
any considerable difference of temperature, whilst there was a great differ- 
ence in the depth at which the observations were taken, this difference rang- 
ing from 2 to 21 meters. 
This important result will, during the coming year, be made the sub- 
ject of new and careful observations, taken as frequently and in as many 
places as possible. If this preliminary result seems to be confirmed, this 
will prove that there is no need of so many stations of observation on 
the Scheldt as we had imagined in the beginning, and that, if, only a 
good point of observation has once been selected, additional observa- 
*See table at the end of this paper. 
