8 THE TANK. 



in diameter ; six inclies is a very convenient size. 

 I have made very pretty vases for minute objects 

 by taking the glass chimney of an Argand lamp, 

 and fastening a well-fitted cork into one end for a 

 bottom, on which I then poured black sealing-wax 

 varnish until a smooth water-tight surface was 

 formed. These are more convenient than wide- 

 mouthed phials, as the sides are more truly 

 perpendicular, and we avoid the unequal re- 

 fraction produced by the thickened bottom of a 

 phial. 



For a conservatory, to which an Aquarium would 

 form an appropriate accessory, a vase-like form 

 might be given to a large tank. If the outline 

 were octagonal, the objects in the interior would be 

 visible through the plate-glass, without the dis- 

 tortion caused by unequal refraction, which is a 

 great objection to vessels with curvilinear sides. 

 But in such a situation, the chief point of view 

 would be from above the surface of the water ; 

 hence the depth should be comparatively small, 

 and the sides might recede, so as to increase the 

 width upwards. 



A good many animals, especially Anemones, 

 Madrepores, Crabs and Annelides, may be kept in 

 broad and shallow pans, in which the water does 

 not exceed three or four inches in depth. The 

 glass pans used for milk are good for this purpose. 

 I have an earthenware pan with upright sides, 

 about five inches deep, in which I have imitated 

 the broken interior of a rock-pool, with irregular 

 projections and promontories of cement. One ad- 

 vantage of such a vessel is that sea-weeds may 

 almost be dispensed with, the extensive surface of 

 water absorbing a large quantity of oxygen from 



