4io 



POPULAR SCIENCE MONTHLY. 



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 some- 

 what 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,. 



Fig. 3. Pools and Wall Tanks. 



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 con- 

 ditions 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 



