136 Treubia Vol. Ill, 2. 



Whenever the windows which open into the aquarium chamber are 

 darkened, this chamber only receives that Hght which penetrates through 

 the tanks and their plate-glass sheets. 



The tanks do not receive their light direct from above, but more 

 from the side. 



It appeared to be difficult to prevent the water becoming too hot 

 by the employment of light straight from above as we get it in Batavia. 



Each of the two rows of tanks receives its light from three windows 

 in the side wall of the aquarium building, which side wall cuts off the 

 accommodation way behind the tanks from the outside world. 



Above these two rows of three windows, that portion of the roof 

 which projects from side walls of the aquarium building consists of glass 

 tiles; the spaces behind the tanks are, moreover, entirely painted white, so 

 that, in these spaces it is very light; in this way the tanks are fully and 

 satisfactorily illuminated. 



The tanks can also be lit up by electric light, by means of lamps 

 placed at the side of the glass panes, just above the water surface. 



In the space. East of the aquarium chamber proper, is in the first 

 place a distilling apparatus, (5, Plan No. 3) and also a tank for distilled 

 water (4, Plan No. 3). 



The object of this is to replace the water which has evaporated 

 during the East Monsoon, from the surface of the tanks, so as to main- 

 tain the salinity constant. 



Evaporation tests, whose results were compared with the data fur- 

 nished by the Royal Magnetic Meteorological Observatory at Weltevreden, 

 show that the greatest evaporation, calculated on the assumption of 

 exceptionally dry weather, with strong winds, and high temperature, barely 

 amounted to one litre per hour for the 200 cubic metres of aquarium water. 



The aquarium of the Laboratory for Marine Investigations has adopted 

 the Lloyd system, in which the same sea water is always in circulation. 



The waste water that comes out of the tanks is cleaned in the cellar 

 of the aquarium before being delivered again to the tanks. 



This circulation is maintained by a pumping set with two reserve 

 installations. 



The two reserve pumping sets are necessary to maintain the circula- 

 tion, owing to the fact it is necessary to pump day and night because of 

 the absence of an elevated reservoir. 



I considered it better to operate this plant without an elevated reservoir, 

 because it did not appear an easy matter to me to protect a reinforced 

 concrete elevated reservoir against the great heat prevailing in Batavia, and 

 also because the cost of an elevated reservoir, so protected, would have 

 raised the cost of construction very considerably. 



The pumping unit, (6, Plan No. 3), on which the duty of maintaining 

 the circulation will fall, consists of a Sulzer centrifugal pump, coupled on 



