CLEANSING AQUARIA. 33 



in the same state for years. It is a common error 

 among those who have had no experience in these 

 matters (and very likely the notion has fostered the 

 idea as to the great trouble which aquaria give) 

 that the water ought often to be changed. Nothing of 

 the kind. A well-balanced aquarium, one that has 

 eventually " got into good working order," wants no 

 water added to it except what may be lost by evapora- 

 tion. If proper care be taken, even this may be reduced 

 to a minimum. The best plan is to have the top 

 covered with a plate of glass. It may be loosely 

 placed there, and ought never to be fastened down, 

 else there would be no means of getting at the con- 

 tents of the aquarium. Such a plate of glass lessens 

 the evaporation, and protects the surface of the water 

 from dust. If we desire that the aquarium should be 

 further ornamental, this may easily be done (with 

 one of sufficient capacity), by having a fountain playing 

 in the middle. Fewer aquatic plants are then required 

 to aerate the water, as the fountain does it mechani- 

 cally, entangling films of air on the surface of every 

 drop of water thrown up. The plants may then 

 be ornamental, such as the water violets (Hottonia 

 palustris), water plantains (Alisma plantago), &c. All 

 that is required is a wide-mouthed bottle, in the cork 

 of which are three holes though which the glass tubes 

 seen in the sketch pass. C reaches nearly to the 

 bottom, whilst the other two pass only through the 

 cork. A is a wide, funnel-topped tube. C is bent at 



D 



