SUNIER: Marine fish-pond of Batavia. 173 
the point of observation lies nearer the sea than the points marked M, but 
not so near as a point marked Z. 
Now the salinity of the water in an empang is influenced: 
1° by the replacing, for the purpose of refreshing the contents of the 
pond, of part of the stale pond-water which has previously been 
allowed to flow away at low tide to the sea, or sometimes to some 
interior water-course on the land side; either 
a: by sea-water admitted at high-tide; or 
6: by brackish or even fresh water admitted from river- or canal- 
mouths or similar waters; 
2° by water being allowed to pass from one pond into another, in 
other words by circulation within the pond-system ; 
3° by the evaporation of the pond-water; 
4° by rainfall; 
5° exceptionally, by inundation or floods; and 
6° probably, by ground-water welling upward. 
When on March 5th 1918 I came to the pond-system represented on 
Map II, the factors mentioned under 4° and 5° had recently made them- 
selves felt. For as a result of the exceptionally heavy rains in February 
1918, large areas of the fish-pond district had been flooded here and 
there by the river-freshets, to such an extent that the bandeng-fish (Chanos 
chanos (FORSK.)) had been able to escape in not a few places. The water 
in nearly all the ponds represented in Table | was, at that time, shortly after 
the river-spates, nearly fresh. Only in pond F, quite near the sea, the 
salinity amounted to 5.5 °/o). This state of things was certainly abnormal. 
After early March 1918 the salinity in all those ponds gradually rose. 
As early as the 19th of March the salinity at all the observation-points but 
one, was between 5.7°/, and 7.9 °/o). Only in pond F situated near the sea 
it had been possible to replace so much pond- water by sea-water, that 
the salinity there had risen to 25.8 °/5). Chiefly in connexion with this sub- 
stitution of sea-water for pond- water, in which process the circulation within 
the pond- system by means of the little sluice-gates (cf. Map II) in the na- 
ture of the case plays a part, the average salinity in the whole of the pond- 
system continued to increase during March, April and May i918. While 
this was going on, the salinity in the inner ponds towards the land con- 
tinued lowest, that in the outer ponds near the sea being highest. 
Local decreases of the salinity, such as took place in the period from 
April 3rd to May 28th 1918 especially in the outermost ponds, F at point 
6, and G at point 7, are bound up with the exchange of water between 
the ponds in question and those situated more towards the interior. That 
such decreases of the salinity are unrelated with rainfall is already 
apparent from the fact, that they do not hold good for the entire pond- 
system. Moreover it appears from information supplied by the Royal 
Magnetical and Meteorological Observatory at Weltevreden concerning 
