CHAPTER II. 



THE TANK. 

 ITS NATURE AND CONSTRUCTION. 



j^^^'E have already stated that a proper vessel, so 

 fitted up with animal and vegetable life, in 

 water, that the liquid need never be changed, is 

 called an Aquarium. We have also mentioned that the 

 vessel in question is called a tank,'^ no matter what its 

 shape, or of what materials it may be composed. There 

 are tanks of all sizes, all kinds, and all characters. A 

 wide-mouthed vial forms one of a simple kind. The 

 chief objection to it is the unequal refraction occasioned 

 by the thick bottom. The sides not being, always, per- 

 fectly perpendicular, is an inconvenience to the tiny 

 rock work or other marine architecture it might be desir- 

 able to introduce. Occasionally, as a toy, a lamp-glass, 

 or the glass-chimney of an argand burner is adapted for 

 the purpose. A cork is fitted tightly into one extremity, 

 and covered on the inside with black sealing-wax varnish, 

 to make it water- tight. On a slightly larger scale, ama- 

 teurs sometimes select a bell-glass with cylindrical sides, 



22 



