Page:The Book of the Aquarium and Water Cabinet.djvu/64

54 a clear view of the bottom, and a vase does not admit of this unless we look from above, the amount of refraction being very great at the base of the vessel. Hence, though marine stock may be well kept in vases, it must be borne in mind that such vessels are far inferior as to the means of inspection to rectangular tanks.

It is also important to bear in mind that marine stock invites the use of the microscope in a greater degree than river specimens, and a flat-sided vessel is the only one which affords proper facilities for the application of a magnifier to its contents.

Stained Glass.—But there is a still more important matter requiring notice here. We are indebted to that accurate observer, Mr. Warington, for valuable information on the effects of light upon certain forms of sea weeds, and his mode of overcoming this is by passing light through variously coloured media. It can easily be understood, that plants, whose natural habitat is at a considerable depth beneath the surface of the ocean, bear exposure to the full daylight very indifferently, and that some special arrangements are necessary in order to cause the solar rays to fall upon them as nearly as possible in the same manner as in the twilight recesses from which they have been removed. This is accomplished by fitting that side of the tank, which is intended to be placed next the window, with a sheet of glass stained of a soft sea green, and the softened light, so admitted to the tanks, promotes the healthy growth of the Algæ, and very materially increases the beauty of the vessel as seen from the other side. Mr. Lloyd, whose ripe experience ever