TEMPERATURE OF WATER.

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temperature are both too powerful, we cannot expect other than the utmost disorder and zoological anarchy. Mr. W. R. Hughes, speaking on this point, says, "It is certain that light is the primary question to be considered in relation to aquaria. The presence of an uninterrupted volume, combined with a high rate of temperature, may in a few days convert an aquarium, which was in an efficient condition of health and beauty of the inhabitants, into a decomposing mass." Moreover, so auxiliary is the effect of light or heat respectively, that it is necessary to reduce the light admitted to a tank when the temperature is rising. Fifty degrees, or from that to fifty-five is about the highest heat which should be allowed; and the light should be toned down as the water reaches the higher point. Mr. Lloyd insists with great emphasis upon the necessity of keeping the temperature low, and this, he contends, can only be effectively done by having a store of water several times the bulk of that in the show tank.

It is evident that, do what we will, some of the sea water cannot fail to be evaporated during the process of fountain or syphon aeration; or even when the surface only is exposed to the air. But it should be remembered that what is thus lost by evaporation is only the fresh part of the water. The salts are left behind—we cannot evaporate them; and so they tend to render the remaining water all the salter and denser. Hence there is an immediate necessity for

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restoring the quantity of water lost, by adding a supply of fresh water. Distilled water is the best to replace the evaporated, as then we know no germs or other interfering agents are likely to be introduced.

In constructing a marine aquarium there is no doubt whatever that pure sea water is the best. This can now be obtained through dealers, or the student may obtain it for himself, always taking proper precaution that the barrel or other means of conveying the salt water, contains nothing that would render it obnoxious. Always use the water as soon after getting it as possible, and do not allow it to remain in wooden. vessels which may discolour it. When placed in the aquarium, add the Ulva, Cladophora, or other useful, oxygen-yielding sea-weeds; and let them grow before putting in any animals. When you think the water is fit, place in a few sea-anemones, adding them one at a time. It is much better to proceed slowly, than to be in a hurry, and have all the work to do over again. Mr. Gosse showed that it was possible to manufacture sea water, and gave the following formula for it :

which should be added to a little less than 1 gallon

of distilled water. This artificial "sea-salt" is now

ARTIFICIAL SALT WATER.

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specially prepared for aquarium keepers, and may be purchased at the natural history dealers. We confess, however, to a disinclination to its use, although we have seen some healthy and beautiful marine tanks, full of life and vigour, supported by water prepared in this manner. At Berlin and Hanover, the marine tanks have their sea water manufactured artificially. The best way to use it, after mixing carefully in an earthen jar, is to allow it to stand in a quiet place, with a few sea-weeds thrown into it, and afterwards expose it to the sunlight. Strangely enough, spores will then develop in it, having come from the atmosphere; or been given off by the sea-weeds. Owing, however, to the conveniences which railways and railway excursions now afford, almost every intending aquarium keeper can get his own sea water from the sea itself.

Sea water can easily be made to indicate the relative saltness or otherwise by using the "specific gravity beads," sold by London dealers. There are two kinds of them, both in the shape of pretty thin glass balls. One of these floats when the water is of the right strength, and the other sinks. Directly the floating ball begins to sink it indicates that the water is weak in saline matter; whilst if the sinking bead rises, it is time to add a little fresh water until it falls again. Both these kinds of balls, or floats, are used in small tanks, and they are usually differently coloured, so as to be soon recognised. A good

hydrometer, however, is much easier to use, and is altogether better.

Undoubtedly one of the charms of marine aquaria

consists in the personal collection of the objects.

SELF-ACTING AIR-CAN.

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Most people have now their annual seaside "run," and it is a poor place indeed if it have no rockpools and no marine animals and plants there to be captured, stowed away, and brought home as souvenirs of pleasant summer rambles. We have known a good many instances, however, in which the animals thus collected have been lost for want of a

proper means of keeping them until they could be transferred to the tank; and we therefore give the accompanying sketch of Mr. A. J. R. Sclater's "selfacting air-can," as one of the best contrivances we have hitherto seen for keeping aquatic objects, whether marine or fresh water. The following is the ex

planation of its structure:

A is the cover of the can; B the socket to fit the cover; C the body of the can; D D plate with perforated raised zinc, showing the water forcing itself into the chamber F, and then going back into the can again; g the top of the cover, which rests on line h, sinking down one inch below upper rim, so that water forcing its way through the upper cover plate also goes back into the can again through the holes, as marked in cover on the under drawing ii; j shows the hollow, and how it is fastened to the left side by a leathern strap k k passing over the head to right shoulder. It can thus be worn when riding or walking. LL is the cover of the can closed down into the socket; mm tin loops to pass the leathern strap through; n n pillars to hold the under plate of cover;