Artificial sea-water may be used instead of the natural. A rough imitation is formed by mixing 100 oz. of fresh water with 3 oz. common salt, 1 oz. of Epsom salts, 200 grs. of chloride of magnesium, and 40 grs. of chloride of potassium.

Or, more precisely, the real constitution of sea-water may be imitated in the following manner: - Mix with 970,000 grains of rain-water, 27,000 of chloride of sodium, 3600 of chloride of magnesium, 750 of chloride of potassium, 29 of bromide of magnesium, 2300 of sulphate of magnesia, 1400 of sulphate of lime, 35 of carbonate of lime, 5 of iodide of sodium. These all being finely powdered and mixed first, are to be stirred into the water, through which a stream of air may be caused to pass from the bottom, until the whole is dissolved. On no account is the water to be boiled, or even heated.

Into this water, when clear, the rocks and seaweed may be introduced. As soon as the latter are in a flourishing state, the animals may follow. Care must be taken not to have too many of these, and to remove immediately any that die. The loss by evaporation is to be made up by adding clean rain-water. The aquarium, whether of fresh or of salt water, will require occasionally artificial aeration. This may be done by simply blowing through a glass tube which reaches to near the bottom; or, better still, in the following way: - Take a glass syringe which can be easily worked. Having filled it with water, hold it with the nozzle about 2 inches from the surface of the water in the acpiarium, into which the contents are to be discharged quickly, and with a sort of jerk. By this means a multitude of small bubbles are forced down into the fluid. This operation should be repeated for a considerable number of times.