Page:The aquarium - an unveiling of the wonders of the deep sea.djvu/316

Rh smell which is perceived on lifting the cover, especially if there be many sea-weeds in the Tank.

Aspect.—The free access of light to the plants is indispensable, and therefore that situation is the best where the sun's rays fall most freely on their leaves. It is beautiful to see the thousands of tiny globules forming on every plant, and even all over the stones, where the infant vegetation is beginning to grow;—to see these globules presently rising in rapid succession to the surface all over the vessel, and to see this process going on uninterruptedly as long as the rays of the sun are uninterrupted.

Now these globules consist of pure oxygen, eliminated by the vegetation under the stimulus of light; and as this is the vivifying principle of animal life, the importance of the process will be readily acknowledged. The difference between the profusion of oxygen-bubbles produced on a sunny day, and the paucity of those seen in a dark, cloudy day, or in a northern aspect, is very marked.

Yet there is one caution required. In summer the heat of the solar rays is very great, as well as their light; and if the vessel be small, and the volume of water very limited, it will become tepid in the midday sun, and the animals will be killed. Hence in a fierce summer day, it will be desirable to interpose a curtain of muslin, oiled-paper, or ground glass, which will break the full power of the rays, without greatly interfering with their illumination.

Cost.—On this point a hint or two, the record of my own experience, is all that I can give. If an Aquarium of considerable dimensions be required,