THE PUBLIC AQUAEIUM 



281 



results have been such as to indicate that this method of aerating 

 and cooling may safely supplant the ordinary method of cooling by 

 refrigeration with a closed circulation. Good aeration apparently 

 is of more importance to Salmonicloe than mere cooling. The nat- 

 ural limit of endurable temperature can not be disregarded, of 

 course. With an electric fan blowing on the numerous jets the 

 temj^erature can be lowered about 4° at any time. The fan seldom 

 is used, and only when summer water temperatures are highest. In 

 addition to the aeration by strong jets at the surface, each trout 

 tank has the usual water supj)ly at the bottom. 



GRAVITY FILTER FOR SEA WATER 



The Jackson gravity filter installed in 1908 in connection with the 

 reservoir of stored sea water has proved satisfactory in every way. 



Fig. 20. — Filter bed of lead pipes half bedded iu cement, the exposed surfaces 

 liaviug inuuinerable tiue crosswise saw cuts tu secure rapid drainage. Three 

 of the small air pipes are visible 



It would be difficult to find a simpler and more effective type for 

 aquarium purposes. It continually carries off the overflow of 55 

 exhibition and reserve tanks, returning the water to the reservoir 

 cleared of all matter likely to affect its purity or transparency. The 

 entire floor in each of the 2-section, concrete, filtering chambers 

 is covered with closely laid horizontal pipes of lead, half sunk in 

 the concrete of the floor. The exposed upper surface of each pipe 

 has many crosswise cuts made with fine gV-inch fret saws, which 

 permit a rapid drainage of water without loss of the overlying quartz 

 sand. There is a central line or header of 4-inch lead pipe in each 

 section, with 42 branches of li^-inch pipe extending to the wall on 

 each side. 



The drainage from the exhibition tanks is carried in a 4-inch pipe 

 across each filter above the bed of sand, the water escaping through 



