THE SALT-WATER AQUARIUM. 
THE SALT-WATER AQUARIUM. 
One of the most delightful amusements of the day, for boys, is the fitting 
up and stocking an aquarium, or mimic fish-pond. The aquarium is a tank, 
wherein the fish and water vegetables are placed—the one to consume car¬ 
bon and give out oxygen, and the other to consume oxygen and give out 
carbon, in such proportions that the water is always kept pure. In the 
aquarium, by an imitation of nature, you have a miniature fish-pond, wherein 
the habits of fish and the growth of sub-aqueous vegetation are laid open 
to the observer, so as to afford him continual amusement. 
THE PRINCIPLE OF THE AQUARIUM. 
The salt-water aquarium is a miniature sea, and the fresh-water aquarium 
a miniature pond. Both, to be real aquaria, must have in themselves the 
power of keeping vegetable productions fresh and growing, and animals 
alive, without the necessity of changing the water. The few cubic feet of 
water enclosed in the glass box must remain pure from month to month, 
kept so by the animal and plant life therein existing; and so soon as any 
appearance of decay in the plants, or of unusual mortality among the live 
inhabitants is observed, it may be taken as a sure sign that something is 
wrong in the structure or condition of the little world. 
The principle upon which the aquarium, either of sea or fresh water, is 
founded, is the following: A plant immersed in water will, under the influ¬ 
ence of light, exhale oxygen gas; and this oxygen it is that all fish and 
marine and fresh-water animals require to sustain life. When goldfish are 
kept in a bowl, they would soon die if the water were not continually 
