Page:Popular Science Monthly Volume 58.djvu/417

Rh about in the tanks. Now they are a dirty brown, now they change to alternating blotches of black and white, and presto, they are pure white. The Red-snappers and Yellow-tails change in the twinkling of an eye so as to be almost unrecognizable. Nearly all these fishes may emit flashes of light apparently at will.

The Cow-fish and its relative the Trunk-fish always excite the interest of the visitors, who are amused at their triangular, box-like bodies and odd manœuvres. Equally attractive are the Morays, of which two varieties are shown; the beautiful Speckled Moray and the great Green Moray. The specimens of the latter now in the Aquarium measure, respectively, seven and one-half feet and six feet long.

The collection of coastwise fishes is excellent, and it contains many rare and little-known varieties, such as the weird Moon-fish, the Spadefish, the Crevallé, the Orange file-fish and the Barracuda, as well as the common food fishes of the markets.

The first requisite of an Aquarium is water, and, while very small aquaria may be, and are, successfully maintained without changing the water, by the use of plants to supply oxygen, this system would not answer at all for large tanks. In England and on the Continent many of the large aquaria store great quantities of water, both fresh and salt, in dark reservoirs, and use it over and over again, filtering and aerating it each time.

In the New York Aquarium this system is not used. Fresh and salt water are supplied to the tanks but once and carried away to the sewer. The fresh water is furnished from the city water mains. The salt-water supply was originally taken direct from the harbor, but, while digging in the cellar to lay a foundation, the workmen pierced a layer of hardpan clay, and water rushed into the excavation. Pumping did not lower it, and tasting proved it to be salt. It was at once utilized as a source of supply and proves to be excellent. The layer of sand underneath the clay is an immense filter bed that removes all suspended matter and furnishes clear, limpid water in unlimited quantity.

Both kinds of water are pumped into large reservoirs and flow thence by gravity to the tanks. Some of the piping is gutta-percha, but practice has demonstrated that first-quality galvanized iron pipe is entirely satisfactory, and it is largely used. Between the reservoirs and the tanks are devices for regulating the temperature, and these are necessitated by the extreme diversity of the collection.

In the summer, the fresh water supplied to the salmon family must be kept down to 55° F., while in winter the tropical salt-water fishes demand 70° F. The former is maintained by an ordinary refrigerating machine, the latter by utilizing the waste steam from the radiators and the pumps.

The exhibition tank, like much of the plant, is the outgrowth of