When this form of rock-work is decided upon, the Aquarium should be of rather wider proportions than usual, in order to allow of the slope being pretty gradual. Supposing the tank to fill entirely the recess of a spare window, which is a position in which it looks exceedingly well, a solid slate back may be found to darken the vessel or the room too much; in such a case, a glass back must be preferred, which can be shaded from the direct influence of the light by a blue or green shade of calico neatly fitted to the frame; and it must be borne in mind, as essential, that the Aquarium must be so placed as to receive the direct rays of light during some part of the day, being screened by a white blind when the sun may be too powerful; as should the water become tepid, it would be fatal to many of the inhabitants of the miniature sea.
With due observance of these precautions, the amateur may hope to frame and establish an Aquarium in a suitable form, and in a suitable position for the reception of its inmates; an account of which, and of the manner of their introduction, will form the subject of the ensuing chapters.
CHAPTER IV.
THE VEGETATION OF THE MARINE AQUARIUM.
As the forest must be planted before its denizens can luxuriate in its shades, so the submarine shrubbery of the Aquarium must be perfected before the aquatic animals can be introduced. For it has been shown, in tracing the history of the experiments which resulted in the establishment of the principles that regulate the formation of Aquaria, that it is by plants only that a supply of oxygen can be kept up, sufficient for the health and existence of all forms of animal life beneath the water.[[1]] It is necessary, also, that the rays of sunlight should fall upon the foliage directly through the surface of the water; and when an Aquarium, with its plants, is placed in a position to receive the light in this manner, their fronds may be observed giving forth the gas in small silvery bubbles and corruscations, which have a brilliant and gem-like appearance.
[1]. Analogous principles are at work in our fields and forests, but we have now only to do with the submarine production of oxygen.
Some marine plants appear to succeed much better than others, but I believe that happens only from their treatment being imperfectly understood; and I believe, not only that all the exquisitely beautiful marine Algæ of our own shores may be successfully grown, but also that the more splendid varieties of the tropical seas may be made to thrive in properly-heated Aquaria, and thus form one of the most attractive features of our hot-houses—one that has not yet been dreamed of.