10 THE FRESH-WATER AQUARIUM. 
aquarium, in the merest outline. Still, brief as this 
chapter must be, I must here impress upon the mind of 
the beginner, that unless the leading features of the theory 
are borne in mind, success can never be achieved in the 
establishment of water collections of any kind. 
If a tank requires frequent cleansing, or frequent 
changing of water, if the fishes come to the surface for air, 
or perish through the presence in the water of offensive 
matter—in fact, if the whole affair has not a distinctly 
self-supporting character, such as will preserve its purity, 
and strength, and beauty, without alteration of any kind— 
it must be concluded that it has been either unskilfully 
stocked or injudiciously managed. 
It is my object to explain briefly, but clearly, the whole 
rationale of aquarium management, whether the tank be 
adopted as a mere ornament—than which there is nothing 
more beautiful—or as a museum of instruction and a school 
of study—than which there is nothing more suggestive, 
nothing that can afford finer lessons of the subtlety of the 
forces, or the refinement of the instincts, that give life 
and loveliness to the ‘‘ world of waters.” 
CHAPTER II. 
PROPER KINDS OF VESSELS. 
Rectangular Tanks.—Any vessel that will hold water 
may be quickly converted into an aquarium; but as we 
desire to have at all times a clear view of the contents of 
the vessel, glass takes pre-eminence among the materials 
