but the latter is desirable, because it is important that the light received into the aquarium should be admitted from above, while the dark sides and back give a more natural appearance to the occupants. The framework, if of iron, should be plated to prevent its rusting, as that would injure the plants and animals. If the parts are cemented, Portland cement should be used, as it is freer from impurities than other cements; however, even it should be soaked in water for several days previous to using. In the form of an aquarium, superficial area
Fig. 2.
Cheap Aquarium.
is more important than depth, because, the larger the surface in proportion to the depth, the greater will be the quantity of oxygen absorbed by the water. For household purposes, the cheapest and most convenient vessel for a small aquarium is the common bell-shaped glass used by confectioners to cover cakes. When this is used, green paper should be pasted upon the outside, except on the front, from the level of the water to the bottom. For marine aquaria the bottom should rise a short distance from the front, and continue in an inclined plane to the surface of the water. The bottom of the aquarium should
