COVERING— ASPECT. 



9 



the air. An oval foot-Tbatli of whiteware makes a 

 capital Aquarium. 



Covering. — Within an inhabited room, or 

 wherever there is much liability to dust or soot, 

 as there is necessarily everywhere in cities and 

 large towns, the Aquarium may 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 smell which is perceived 

 on lifting the cover, especially if there be many 

 sea-weeds in the tank. 



In ordinary circumstances, however, there is no 

 necessity for a covering of any kind. My own 

 tanks, though placed in an inhabited room, remain 

 for months together uncovered, in winter and sum- 

 mer, without the least loss of transparency. The 

 dust speedily sinks, and is harmless. 



Aspect. — The free access of light to the plants 

 is indispensable ; and therefore that situation is the 

 best where the sun's rays fall most freely on their 

 leaves. It is beautiful to see the thousands of 

 tiny globules forming on every plant, and even all 

 over the stones, where the infant vegetation is 

 beginning to grow ; to see these globules presently 

 rising in rapid succession to the surface all over 

 the vessel, and to see this process going on unin- 

 terruptedly as long as the rays of the sun are 

 uninterrupted. 



Now these globules consist of pure oxygen^ elimi- 

 nated by the vegetation under the stimulus of 



