134 THE FRESH-WATER AQUARIUM. 
answers many purposes admirably; it is sufficiently trans- 
parent, moderately strong, and quite cheap. One having a 
diameter of twelve and a half inches, with a depth of eight 
inches, and of good thickness, can be bought for two dollars 
and a half; the knob on the top will prevent its standing 
steadily, and to obviate this difficulty a stand can easily be 
turned from a block of wood, with a hole cut in the centre 
large enough to admit the knob, and allow the bottom of the 
glass to rest upon it as a support. If properly taken care. 
of, a tank of this sort will last for years, and be a great 
comfort to its possessor, but an untimely accident will before 
long induce him to try something more substantial. 
- Perhaps the best tank for the aquarium in use is what is 
ealled a rectangular tank, having the four sides of glass, and 
the base of some hard material such as stone, iron or wood. 
The glass is held in place, and supported at the four corners 
by as many pillars of iron or wood, which are held together 
on top by strips of a similar material connecting them. Of 
the three materials for the base and pillars, iron is by far the 
best for a fresh-water tank, if we can have but one material 
alone; it is lighter than stone, and the little it rusts from 
time to time does not amount to anything; the water does 
not ooze through it as it does through some kinds of stone, 
and it does not warp, as wood is so apt to do if the tank is 
left without water for a length of time. To prevent rusting 
a layer of cement may be spread on the bottom of the tank 
inside, and a plate of thick strong glass placed upon it; and 
in the same way a narrow strip of glass‘can be cemented to 
each of the pillars, so that the iron shall be prevented from 
coming in contact with the water at every point. A tank, 
. having a base of slate and pillars of iron protected by glass, 
as just explained, is the best kind of a tank to own, as it can 
be used for either salt or fresh water as we require. The 
shape of a tank, too, is of some importance, that of a double 
cube being the best for this reason, that it allows more of a 
clear surface on the long sides for inspection after the rock- 


