THE FRESH-WATER AQUARIUM. 7 
kinds hitherto the least studied by naturalists, displaying 
to our close gaze their natural forms, and colours, and in- 
stincts, and economy, as freely and as happily as if they 
were still hidden from us in their native depths. In this 
sense, the aquarium remunerates for any trouble it may 
cost, in the lessons it affords of the workings of Almighty 
Wisdom, in those regions of life and wonder to which it 
introduces us. 
The Philosophy of the Aquarium must be clearly 
understood by those who purpose to cultivate it. It is a 
self-supporting, self-renovating collection, in which the 
various influences of animal and vegetable life balance 
each other, and maintain within the vessel a correspond- 
ence of action which preserves the whole. A mere globe 
of fish is not an aquarium in the sense here indicated; 
because, to preserve the fish for any length of time, the 
water must be frequently changed; and even then the 
excess of light to which they are exposed, and the con- 
finement in a small space, in which they quickly exhaust 
the vital properties of the water, are circumstances at 
variance with their nature, and sooner or later prove fatal 
to their lives. 
In an aquarium, the water is not changed at all, or at 
least only at long intervals, as we shall explain hereafter ; 
and besides the enclosure Of fishes in a vessel of water, 
growing plants of a suitable kind, always form a feature of 
the collection. Formed on this plan, an aquarium is an 
imitation of Nature on a small scale. The tank is a lake 
containing aquatic plants and animals, and these maintain 
each other in the water in the same way as terrestrial 
