Page:The aquarium - an unveiling of the wonders of the deep sea.djvu/315

258 liable to break in the manufacture, and also at any moment even after they have been some time in use. Mine, though not free, as I was warned, from the same danger, has hitherto survived more than a twelvemonth's service. The height may be chosen according to taste, as the risk does not depend on this, but on the diameter. Mine is 10 inches high. I cannot commend this form; it is mean and inelegant; and as it is a blown vessel, the sides are not truly cylindrical.

For a conservatory, to which an Aquarium would form an appropriate accessory, a vase-like form might be adopted. If the outline were octagonal, the objects in the interior would be visible through the plate-glass without the distortion caused by unequal refraction, which is a great objection to vessels with curvilinear sides. But in such a situation, the chief point of view would be from above the surface of the water; hence the depth should be comparatively small, and the sides might recede, so as to increase the width upwards.

Covering.—Within an inhabited room, or wherever there is much liability to dust or soot, as there is necessarily every where in cities and large towns, the Aquarium must be protected by a cover. This may be made of fine muslin, or, which is better, of plate or sheet-glass, according to the dimensions required. The latter may simply be laid over the top of the vessel, allowing the escape of gases under the edge. It should be occasionally lifted for a moment, to allow of a change of the superincumbent air:—the necessity of this will be manifest, from the close