SUNIER: Marine fish-ponds of Batavia. 175 
daily highest and lowest water-levels at Tandjong Priok. The data for 
this diagram are derived from the tidal movement, calculated from the 
tidal constants by the Royal Magnetical and Meteorological Observatory 
at Weltevreden. The zero-point of the vertical axis is arbitrary. During 
the 40 days between February 27th and June 17th, and the 36 days 
between August 23rd and November 13th, when in 1918 high and low 
water occurred twice every twenty-four hours at Tandjong Priok, I have 
constantly taken into account the highest high-water level and the lowest 
low-water level. 
The high and low-water levels on the days between those on which the 
maxima and minima, represented in Diagram I, occurred, generally speaking 
do not fall far outside the lines connecting the points traced in Diagram I, as 
appears from Diagram Il in which have been marked the high-water-levels 
for 36 consecutive days with preponderatingiy diurnal tides. 
From Diagram I it appears in the first place that in 1918 the 
difference between high and low water, which varies considerably in the 
course of the year, was never more than 109 cM. (January 11th) 
and never less than 19 cM. (August 25th). I presume it will be obvious that 
the opportunity for replacing pond-water by sea-water will be more favour- 
able, other things being equal, in proportion as the difference between high 
and low water is greater, and less favourable as this difference diminishes. 
A second conclusion to be drawn from Diagram | is that the high-water 
levels vary more than the low-water levels. The strongest variation is ob- 
served in the maxima of the high-water levels (43 cM.), the slightest in 
the maxima ') of the low-water levels (18 cM.). 
In connection with the usual level of the bottom of the ponds 2), it would 
appear that in the pond-system in question it is actually the differences in 
the high-water levels that have the greatest influence on the opportunity 
for replacing pond-water by sea-water. 
On the 27th April 1918 Mr. Görs complained that he had been obliged 
to catch away the fish in pond A of Map II prematurely, in connection with the 
fact that during the last few months he had been practically unable to 
admit any sea-water, as the tide refused to rise high enough. I noted in 
my diary that it was not until between April 27th and May 14th (therefore 
as may be seen from Diagram I about May 12th) that it proved possible to 
admit a little more sea-water here. This was also practicable (at least in 
ponds C, C’, D, E, F, and G at point 7) between July 16th and July 30th 
(therefore as resulis from Diagram | about the 21st July) when consequently 
the salinity in the last-mentioned ponds could again be lowered a little. 
1) By these I mean the low-water levels when the water was highest. 
2) According to the Service for the improvement of the water-supply and drainage in 
the capital of Batavia (Dienst voor verbetering der water aan- en afvoer ter hoofdplaats 
Batavia), the pond-bottom in this part of the fish-pond belt would be mostly at Batavia- 
level or slightly higher. Batavia-level is approximately equal to the average low-water 
level of the Java-sea on the coast of the fish-pond region, 
