become chemically changed, and deprived of their putrescent qualities. This is what takes place in nature. By the perpetual dashing of the waves against the shore, and especially against the ragged rocks, an immense quantity of air becomes entangled, in the form of minute bubbles, which by the various currents are diffused through the sea, and even carried to considerable depths, before they rise to the surface and become dissipated. Thus the violent agitation of the sea is a powerful agent in its purification.
One of the simplest modes by which this object can be effected, is the drip-glass. I have been accustomed to suspend over the Aquarium, a perforated bell-glass (I think it is called a bee-glass) of suitable size, into the orifice of which a bit of sponge may be pushed, or a cork drilled with small holes. The cord which suspends the drip-glass passes over a pulley at the top of the window, so as to be raised or lowered at pleasure. Every morning sufficient water from the Tank is drawn or dipped off, to fill the drip-glass, which is then hoisted to its full height. The contents run out in slender streams, or in a rapid succession of drops, which, passing through some four or five feet of air before they reach the Tank, become effectually purified.
The same purpose may be more efficiently accomplished at a slight expense, in a manner which would greatly augment the elegance of the Aquarium. In the engraving placed at the commencement of this chapter, I have represented a Fountain-Aquarium, a form of the invention particularly suitable for a conservatory or hall. It needs but a vessel fixed, as a
