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the plate not to go below o. Of course it is always best to transfer any captured aquatic objects to their new habitats as quickly as possible. Keeping them in unnatural conditions is cruel, and no true naturalist will inflict pain on the humblest creature if he can possibly avoid it.

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FIRST PUBLIC AQUARIA.

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CHAPTER X.

OUR PUBLIC AQUARIA.

THE establishment of large public aquaria in English cities and towns is the best evidence we could desire of the progress of zoology. There can be little doubt that these important institutions will react favourably on scientific education by familiarising people with objects they were previously only acquainted with in books, and also by stimulating young minds to their further study. Their value to natural history cannot be overstated, for they afford means of observation which never existed before, both to study. the habits and the embryological development of marine animals.

To Mr. W. A. Lloyd belongs the merit of successfully carrying out the idea of large public aquaria to their present issue. No other naturalist has enjoyed such a long and specialised experience in their construction and management, either at home or abroad. The continued success of the Crystal Palace Aquarium -which may be called the first public one of any magnitude, those at the London and Dublin Zoological Gardens and elsewhere being on a much smaller scale-undoubtedly encouraged the construction of

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aquaria at Brighton, Manchester, &c. A full and detailed description of that at the Crystal Palace will be found in the excellent Handbook' which Mr. Lloyd has written.*

In large aquaria it would be utterly impossible to sufficiently aerate the water in the huge tanks by means of algæ. The quantity required to be grown to oxygenate the water sufficient for a very few fish to be healthily kept would be so great that it would almost fill the tanks. Moreover, in these show tanks it is necessary there should be as little as possible to obstruct the observation for which they are constructed. Even if sufficient aeration could be produced by the presence of sea-weeds, that alone would not represent the actual marine conditions by which fish and other animals are naturally surrounded. The seething, restless condition of the ocean-with its huge volume of water moved by tides, currents, and storms, so that the waves raised by the latter are always entangling quantities of atmospheric air all over its broad surface-is best imitated in large aquaria by the circulation which is constantly hurrying masses of water from one place to another, and always

* In 1861 Barnum had two white whales captured for him at the mouth of the St. Lawrence, and conveyed alive to his museum at New York, where they were exhibited in large tanks constructed for the purpose. Other tanks were shortly afterwards constructed by him, in which sharks, porpoises, "angel" fish, &c., were shown. These animals were kept alive by a stream of salt water from high tide. This was the first rude attempt at aquaria in America.

AERATION OF AQUARIA.

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presenting new surfaces to the oxygenating influences of the air. In fresh-water aquaria we need this mechanical aeration and circulation in the same degree, perhaps, although we there imitate the quiet condition of our still ponds and tarns. In our small parlour aquaria, constructed to maintain marine creatures, we also require its assistance, such as may be produced by the means already described; but it should be remembered that here we are only imitating the natural conditions of rock-pools. On the other hand, in the huge tanks seen in every large public aquarium, it is sought to imitate the conditions of the open sea.

A most important mechanical contrivance for aerating aquaria was invented by the late Mr. G. Hurwood, of Ipswich, in 1859. It consisted of an arrangement by which "the pressure of a stream of fresh water, such as exists in the pipes of waterworks in towns, or such as can be got from a high cistern already existing in a dwelling house, may be employed to compress air, which compressed air in its turn forces a current of sea water into an aquarium.” This contrivance was first successfully adopted on a large scale at that erected in the garden of the Acclimatisation Society of Paris, in 1859, shortly after Mr. Hurwood invented it. It was afterwards partly applied by Mr. Lloyd to the Hamburg Aquarium, of which he then had the charge. The sea water in the Hamburg institution was "circulated

partly by a water-pressure engine set in motion by the town waterworks, which drives a pair of waterpumps (instead of compressed air, as was done at Paris), and partly by a steam-engine which drives two other pumps."

Mr. Lloyd's plan of keeping a large underground, dark reservoir for storage purposes, into which the water runs from the tanks after circulating throughout, and from which it starts again on its circulatory round, has been markedly successful. The water is bright and sparkling, and its temperature is thus always easily kept at from fifty to sixty degrees. The aggregate contents of the tanks at the Crystal Palace is only one-fifth of the contents of the reservoir. This readily enables the manager to at once empty any tank into it, should it get wrong, and the slight admixture of the turbid water would be unable to affect the good condition of the general volume. No animals are kept in the reservoir; the main aeration is produced by the mechanical agitation of circulation, and the constant injection of sprays of salt water entangling air into each tank. This is constantly going on, night and day, duplicate steam-engines and boilers being employed, in case of any accident occurring to one of them. The stoppage of this mechanical circulation for some hours is attended by distressing symptoms, and Mr. Lloyd remarks that "the creatures in the tanks, and especially in the taller tanks, must be considered, to some extent, in

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