BULLETIN No. 1. 
HYDROGRAPHICAL INVESTIGATIONS AT 
LAKE TAMBLEGAM. 
By Joseph Pearson, D.Sc, F.R.S.E., F.L.S. 
IN the course of the scientific investigations of the mndow- 
pane oyster fishery at Lake Tamblegam monthlj' 
records have been kept of the specific gravity of the water 
since September, 1915. At the end of each month the Govern- 
ment watcher collects samples of water from eight stations in 
the lake. The samples are placed in special stoppered bottles 
recommended by the International Council for the Exploration 
of the Sea, and are despatched to Colombo for examination. 
The samples are then tested by means of Knudsen hydrometers 
and corrections are applied by means of Dr. Knudsen's 
hydrographical tables.* An analysis of the results thus 
obtained are of exceptional interest as might be expected 
in view of the peculiar geographical position of Lake Tamble- 
gam. This sheet of water is a shallow landlocked backwater 
connected with Trincomalee outer harbour, and has an area of 
nearly six sqiiare miles. It is connected with the sea by a 
narrow channel less than a quarter of a mile across. Flowing 
into the south-western and southern portions of the lake are 
several rivers, many of which are of little or no account except 
during the wet season, while the northern portion of the lake 
receives no rivers. The main portion of the lake is covered 
with soft slimy mud, and has a depth of from 5 to 8 feet. The 
wet season is from November to January, and the rest of the 
year is dry save for an occasional shower. Thus, for two or 
* Cl.=Weight of chlorine in grammes in 1000 grs. of sea water. 
S. =Total weight of salt in grammes in 1000 grs. of sea water. 
■5. =(S — - 1) 1000, where S. = specific gravity of sea water at 0° C. 
referred to distilled water at 4" C. So that a specific gravity of, say, 
1-02542 is given as 25-42. 
6(13)22—350 3 
