oard should have three or four hardwood cleats screwed
to the bottom to prevent warping. The corner pieces of our glass box
may either be made of sheet copper or heavy tin, or of wood, if we
cannot work in metals. The wooden strips and the bottom board should
have grooves ploughed in them to hold the glass. All the woodwork
should be given several coats of asphalt varnish and to further
waterproof it and as a final coat use some kind of marine copper paint
that is used to coat the bottoms of vessels. Never use the common
white lead and linseed oil paint for an aquarium.

You can sometimes buy aquarium cement or prepared putty at a "gold
fish" store. This you will need to putty in the glass. If you cannot
buy it, make it yourself from the asphalt varnish and whiting. Be sure
that the paint and putty of an aquarium is thoroughly dry before you
fill it with water.

Perhaps the most satisfactory way to study fish and insect life in
water is to use all glass boxes and globes. So many kinds of fish and
insects are natural enemies, even though they inhabit the same
streams, that they must be kept separate anyway. To put them in the
same aquarium would be like caging up two game roosters. If we were
studying the development of mosquitoes, for instance, from the larvae
or eggs to the fully developed insect, we should not get very far in
our nature study if we put them in an aquarium with fish. A fish will
soon make short work of a hundred mosquito wigglers just as a large
frog will eat the fish, a snake will eat the frog and so on.

Rectangular glass boxes such as are commonly used for aquaria cost
less than a dollar per gallon capacity. Goldfish globes cost about the
same. White glass round aquaria are much cheaper and those made of
greenish domestic glass are the cheapest of all, a glass tank holding
eight gallons costing but two dollars.

[Illustration: A self-sustaining or balanced aquarium]

Any transparent vessel capable of holding water, even a Mason jar will
make an aquarium from which a great deal of pleasure may be derived.
The old way of maintaining aquaria in good condition required a great
deal of care and attention. The water had to be changed at least once
a day if running water was not available, and altogether they were so
much trouble that as a rule owners soon tired of them.

Modern aquaria are totally different. By a proper combination of fish
and growing plants we can almost duplicate the conditions of