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262 they will tinge the water after any amount of washing, the former with lime, the latter with ochre.

Small pebbles or fine gravel, likewise well washed, may be used to vary the bottom with the sand.

Masses of rock, of dimensions suitable to the Aquarium, should be put in to afford shelter and concealment to such animals as like the gloom. To afford this in the highest degree, a flat piece may be set, like a table, or cromlech, upon two or three upright blocks; or two tall pieces may lean against each other, forming a rude arch;—care being taken, whatever arrangement be chosen, that the masses stand with stability. It is of little consequence what sort of rock is selected,—limestone, sandstone, granite, conglomerate,—but the rougher, and the more full of cavities and angles, the blocks are, the better will be the effect.

Water.—The purity of the water is of great importance. In London, sea-water may be easily obtained, by giving a trifling fee to the master or steward of any of the steamers that ply beyond the mouth of the Thames, charging him to dip it in the clear open sea, beyond the reach of rivers. I have been in the habit of having a 20 gallon cask filled for me, for which I give a couple of shillings.

The vessel in which it is conveyed requires attention. A cask is the best, if a considerable quantity of water is required; but it is absolutely indispensable that it should be either new, or at least that nothing injurious should have been previously contained in it, such as spirits, wine, chemicals, acids, &c.; since no soaking will prevent hurtful qualities from being communicated to the water. Even the bungs ought to be