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same journal of March 24 last. If it be urged that small, reservoirs may be made to do as makeshifts, because money and space for them cannot be afforded, there is some kind

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of reason in that. But if it be averred to the contrary as a principle, then that indicates a singular amount of no knowledge which, if possible, is something more than won

derful. My arguments are founded on the clear and simpleobviousness of the fact that a given quantity of dead organic matter diffused through a large quantity of water sullies it less than if it were small, and on the necessity of maintaining an evenly moderate temperature for the reasons already given, avoiding the high and low ranges of the atmosphere; and I show that the easiest manner of attaining this is by having a large reservoir sunk in the earth at a distance giving a known temperature. Thus, referring to the sunk thermometers at the Greenwich Observatory, with a thermometer having its bulb on a level with the scales of the sunk instruments, the lowest (January) mean monthly reading in a named year was 36.4° F., with a mean daily range of 6.9° F.; and under the same circumstances the highest (July) mean monthly reading was 66.9° F., with a mean daily range of 19.9° F. But from the showing of other thermometers whose bulbs are sunk in the ground to the respective depths of one inch, three feet, twelve feet, and twenty-five feet, the temperatures become strikingly even for the whole year through-so much so, that at twenty-five feet deep the mean monthly reading of January was 52° F., with a mean daily range of only 0.025° F.; and the mean monthly reading of July was 49.0° F., with a mean daily range of but 0.06° F., the highest mean daily range at that depth in any month of the year being 0·07° F. in August. To apply this to aquaria, I have made the accompanying diagram (p. 261), it being an ideal vertical section of an aquarium, consisting of a show-tank A, with its reservoir в in the earth, with an inlet supply-pipe c, and an outlet pipe D, the six arrows showing the direction of flow of water. E is a pipe supplying water to compensate for evaporation, which, both for marine and fresh-water aquaria, should be distilled water. For simplicity, the engines, pumps, &c., which circulate the water are omitted, the showing of results being alone aimed at.

Supposing that in any part of an English year the temperature of B would be 60° F., and that in summer A would rise to 75° F., that would be much too warm for an aquarium containing British animals. Or it might in winter sink to 30° F. or less, that would be much too cold. But on a sufficient circulation being established between A and B, then their mean temperatures would be expressed by the seven following formulas, varying according to the size of B :

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Indeed if B were one hundred times as large as A, and were kept at 50° F., then a might be in an atmosphere at 212° F. (the heat of boiling water), and yet its water would be only 52.12° F., and the most delicate English animals would live in it. At Nottingham is an aquariam where the show-tank and reservoir spaces have had to be made as 13 is to 1. From Bünsen's tables in his "Gasometry," page 288, may be ascertained the amount of atmospheric air which water in open vessels will absorb at given temperatures, the barometer being at 39"; and I here reproduce his figures, having converted his Centigrade scale into Fahrenheit and Reaumur scale for the benefit of English, German, and Spanish readers.

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And therefore as the more air there is in the water the better it is, hence the value of large and therefore cool reservoirs. Inpedendently of all this, however, the larger the bulk of water, and the more constant and vigorous the circulation and aeration, the less it will be sullied by the animals which live in it. In the Crystal Palace Aquarium we have in the show-tanks 20,000 gallons of sea-water, and in the reservoir 100,000 gallons, total 120,000 gallons, supplied by Mr. W. Hudson in 1870. Yet in this comparatively small quantity of unchanged fluid we have, from Sept. 1871 to March 31, 1876 (four and a half years), given to the animals in it the following enormous quantity of food without the water being otherwise than always sparklingly clear :

The water in the Crystal Palace aquarium has a very small range of from 52° F. in very cold, to 61° F. in very hot, weather. In April last (1876) we had, at Sydenham, blue skies, a bright sun, and an oppressive warmth, with 74° F. in the shade, on the 8th of the month. On the 12th, four days after, we had a leaden firmament, and clouds of blinding snow and sleet driven by a bitter north-east wind, with the thermometer at 29° F., giving so great a range as 45° F. within a week. Yet the water in the aquarium had a range of only 1° F. = 54° F. to 53° F.

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9. Fish, chiefly Whiting (Gadus), in pounds weight.
10. Smelts' roe (Osmerus)

11. Green seaweed (Ulva), purchased

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(Conferva), grown in tanks, quantity unknown.

And, in addition, we obtain occasional and unrecorded supplies from neighbouring fishmongers when the regular supply runs short. Of this animal food, all but the denominations 9 and 10 are kept alive in a series of reserve tanks till the moment of being eaten. Scarcely any uneaten food, and never any excrement, is manually removed; but all which is not consumed by the animals is chemically dissipated, without filtering, by the enormous volumes of air constantly being injected into every tank by Leete Edwards and Norman's machinery, the speed of which is accelerated (i.e. the oxygenation is quickened) when the water is slightly turbid from an excess of organic matter. All this I have explained more at length in the "Official Handbook to the Crystal Palace Aquarium," and in "Observations on Public Aquaria,” both published at the Crystal Palace. It is this power of oxygenating, or consuming, or burning, at a low temperature, termed by Baron Liebig "eremacausis," "* which expresses the real work done in an aquarium, and the force necessary to do that work. Even our thick beds of sand and shingle at the bottoms of each tank are so fully charged with air, that one thrust of a stick will release a pint of it in bubbles. This is a source of purification and health quite unknown till recently. Consequently the floors of our tanks (excepting the sea anemone tanks) are as speckless and as free from the blackness caused by sulphuretted and carburetted hydrogen gas, as on the day they were laid down in 1870. If we have an excessive growth of seaweeds anywhere, we turn in a shoal of grey mullet (Mugil capito), who nibble it down close, like sheep in a field of grass. This leads me to say that at present we do not know how to grow the higher marine algæ, the red, the brown, or even the

From the Greek "to remove by burning, or by fire." The words "caustic" and "cautery " have the same derivation.

green kinds, at will. Sometimes I succeed, but always by chance, not knowing why.

Of the general influence of aquaria on Zoology we have curious evidence in Mr. Gosse's most excellent "Manual of Marine Zoology for the British Isles," published in two volumes, in 1855-1856, in which the author enumerates 1,785 species, from sponges to fishes, and of which he figures 779 genera, always preferring to draw from living animals whenever possible. Now, as at that period a larger number of aquarium animals had passed through his hands than through those of any other person, he may be presumed to have, up to then, seen more of them alive than anyone else. Yet he enumerates only 201 as having been drawn from life, as he avowedly preferred doing, and of these but a dozen were fishes, others being, for the most part, small creatures, or those which are easily maintained, and do not need large tanks and elaborate machinery. But, during the twenty years which have elapsed since 1856, I have seen and handled, and had under my care, in England, France, and Germany, about 433 species of British marine animals, of which 112 were fishes.

There are few things more trying to that great virtuepatience than a large public aquarium, especially in its preparation, before it is ready for the reception of animals. It is to this lack of patience on the part of the directors of the Royal Westminster Aquarium, and to their absolute refusal to allow me to have proper engineering assistance during its construction, and to general mismanagement, that its present confused state, and its unsatisfactory condition in every way, is due. On this account, I resigned my post of adviser to the society, as I found it useless to advise when advice was recklessly disregarded. Aquarium work, being hydraulic engineering on a small scale, is essentially the work of an engineer, and not that of an architect, unless he is also an engineer and a mathematician. There is for aquaria a great and important future, both as regards their influence on science, and as pecuniary speculations, if indeed, as I much doubt, there can be any real severing of these two interests. Success, however, must always be the result of a careful study and representation of what nature does, and of a strict avoidance of the recent heresies to which I have in this communication adverted.

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