258 THE COVERING. 



liable to break in the manufacture, and also' at any 

 moment even after they have been some time in use. 

 Mine, though not free, as I was warned, from the 

 same danger, has hitherto survived more than a 

 twelvemonth's service. The height may be chosen 

 according to taste, as the risk does not depend on 

 this, but on the diameter. Mine is 10 inches high. 

 I cannot commend this form ; it is mean and inele- 

 gant ; and as it is a blown vessel, the sides are not 

 truly cylindrical. 



For a conservatory, to which an Aquarium would 

 form an appropriate accessory, a vase-like form might 

 be adopted. If the outline were octagonal, the objects 

 in the interior would be visible through the plate-glass 

 without the distortion 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. 



Covering. — Within an inhabited room, or wherever 

 there is much liability to dust or soot, as there 

 is necessarily every where in cities and large towns, 

 the Aquarium must be protected by a cover. This 

 may be made of fine muslin, or, which is better, 

 of plate or sheet-glass, according to the dimensions 

 required. The latter may simply be laid over the top 

 of the vessel, allowing the escape of gases under the 

 edge. It should be occasionally lifted for a moment, 

 to allow of a change of the superincumbent air : — the 

 necessity of this will be manifest, from the close 



