INTRODUCTION. 21 



a too rapid growth of green vegetation, induced by the 

 action of light. This may be corrected by depriving the 

 vessel of light for a few days. 1 have seen a tank at Lloyd^s 

 restored to perfect clearness by being covered over for a short 

 time with dark cloths. 



For the purpose of occasional aeration a drip-glass is 

 recommended. A bell-glass perforated, with a piece of 

 sponge lightly put into the hole, is suspended over the tank, 

 and water taken from it is put iu and allowed gradually to 

 drip through. A fountain- Aquarium, with apparatus for 

 drawing the water up into the reservoir, would be a very 

 good contrivance. This would save all the trouble of baling 

 the water out of the tank, at the risk of disturbing the 

 living organizations within it. A small pump, drawing the 

 water through fine holes from near the bottom, would effect 

 the purpose. The unsightHness of the apparatus could be 

 disguised by rockwork, and the fountain, assuming the 

 form of a cascade, might be so placed as to present an ele- 

 gant object. 



In conclusion, it is hardly necessary to recommend this 

 new and popular method of studying Nature, as a prolific 

 source of amusement and instruction. But although I have 

 not in these pages followed the fashion of making Natural 



