Page:Popular Science Monthly Volume 58.djvu/418

410 experience and failure. The front is made of plate glass nearly an inch thick, and this is fastened into a strong frame of iron, which, in turn, is firmly secured to the building. The joint between the glass and the iron must be water-tight, of course, but it must also be somewhat flexible, to accommodate the changes due to temperature and the bulging due to pressure. It is made by wedging the glass into a rebate with strips of dry basswood as firmly as possible; when these become water-soaked they swell, so as to make the joint perfect, and. yet to allow the necessary play. To the rear side of the iron frame is bolted a wooden tank, narrower at the bottom than the top, and when this is in place it is given a coat of Portland cement for a lining. This lining gives a pleasing neutral tint for a background, is very clean, and,

should occasion demand, it may be readily replaced. The largest glass used is ninety by forty-eight inches for a single tank, but in some cases two tanks are thrown into one by cutting the partition walls, as shown in the shark tank (Fig. 3).

Between the exhibition tanks and the outer wall of the building is an annular corridor devoted to the purposes of administration, and to this the public is not admitted. Here the keepers and their helpers are occupied almost constantly in the multifarious duties that the conditions of maintenance impose; here the pumping machinery and the temperature-regulating apparatus are located, and here are the tanks that hold the reserve stock and those used for hospital purposes.

Cleanliness equal to that found on a private yacht is maintained, as a matter of course, and lies at the foundation of the uninterrupted