THE AQUARIUM, APRIL, 1897. 99 

THE PRINCIPLES OF THE AQUARIUM. 
Whether the scientific principles 
upon which the success of an aquarium 
is based were already understood by 
the ancients, is not known and now 
hard to prove. Atany rate, the present 
manner of sustaining an aquarium 
through the action of aquatic plants 
without change of water, is based on 
Ingenhauss’s discovery, made in the 
second half of the eighteenth century 
that © plants when exposed to the action 
of light emit an air which he announced 
as oxygen gas.” 
Fish inhale the oxygen contained in 
the water and exhale in turn a gas 
called carbonic acid gas, a very poison- 
ous compound ; this the plants inhale, 
and, appropriating the carbon to build 
up their own tissues, give off the oxy- 
gen again for the fish, so that this gas 
oxygen becomes but a carrier of carbon 
from the animal economy to that of 
the vegetable. When the sun shines 
on the plants in our aquarium, very 
often their leaves will be seen to be 
covered with an innumerable assem- 
blage of minute globules of that gas, 
glistening like dew-drops upon grass. 
Carbonic acid gas is heavier than 
oxygen. It is the same body that col- 
lects in wells and in some of our mines 
and which is also given off from stoves, 
often causing disease and death. When 
this gas is present in too large a quan- 
tity the fish feel uncomfortable at the 
bottom, they go near the surface of the 
water and finally are forced to breathe 
the oxygen contained in the atmos- 
phere. 
This discovery, like many useful 
others was from year to year improved, 
and could these scientists of bygone 
days see the parlor aquarium of Amer- 
ica to-day, inhabited with plants and 


animals from every zone of the globe, 
see fishes and amphibians bred in 
them, not solely by protessionals, but 
likewise by lady amateurs, observe the 
joy it creates in the child, the in- 
valid, or the sick in the bed chamber, 
they would justly feel proud, for they 
were unknowingly great benefactors to 
man. 
LOCATION FOR THE AQUARIUM. 
An aquarium is also very beneficial 
in improving the sanitary condition of 
a living or bed room through its purify- 
ing influence on the atmosphere. All 
the impurities of the air are absorbed 
by the water, this is in turn purified by 
the plants and the water evaporating 
into the room is perfectly pure. 
As we have seen above, the founda- 
tion of an aquarium is the plant life. 
When one has concluded to get an 
aquarium into his house, the first thing 
that should be considered is the location 
of the tank. 
The best side of a room for the aqua- 
rium is that having a window near 
which it is to be placed, as the light 
can be increased or reduced by regu- 
lating the shades accordingly. The 
best exposure is that towards the North ; 
by such an exposure the aquarium 
should stand about six inches away 
from the window; next best is one 
towards the East, the best distance in 
such a case is about twelve inches from 
the window ; next best is a window fac- 
ing South or West, here set the aqua- 
rium about eighteen inches towards the 
room, and when the windows are high 
even more space may be left between 
(see illustrations pp. 86-88). 
When an aquarium is to be located 
between two windows, it should be far 
enough in the room to receive the light 
from both, and in a corner room with 
