MINIATURE CIRCULATING SYSTEMS FOR SMALL LABORATORY AQUARIUMS 53 



erable range. This is because, as the water 

 rises, it occhides the open end of the down- 

 facing tube. There is a slight negative 

 pressure in this tube caused by the outflow- 

 ing water in the constant-level part of the 

 siphon. Thus, as the water rises in this 

 accessory tube, the whole system becomes 

 a simple siphon with two inlets, obliterat- 

 ing the constant-level feature. This in- 

 creases the flow considerably, the amount 

 being related to the length of drainpipe 

 attached to the horizontal arm of the tee. 

 The w^ater level in the aquarium thus falls 

 rapidly and the end of the inverted U 

 tube is reexposed and the system regains 

 its constant-level feature. 



In practice, if the inflow of water to the 

 aquarium is slightly more than the con- 

 stant-level siphon will carry off, the water 

 level in the aquarium will be at the mouth 

 of the open tube. This tube will normally 

 suck water from the surface and air, 

 through a considerable range of inflow. 

 Incidentally, this condition effectively re- 

 moves any scum that may form on the 

 surface. 



The basis of this item was received from 

 a correspondent shortly after the appear- 

 ance of the 1957 issue of this paper. Un- 



fortunately, the name of the individual 

 concerned is no longer available, and it is 

 therefore impossible to credit him prop- 

 erly here by name. 



LITERATURE CITED 



Breder. Charles M., Jr.. and Thomas H. 



How LEY. 



1931. The chemical control of closed circu- 

 lation systems of sea water in aquaria for 

 tropical marine fishes. Zoologica [New 

 York], Vol. 9, No. 11, pp. 403-i42. 



Bredeb, Charles M., Jr., and Homer W. Smith. 



1932. On the use of sodium bicarbonate and 

 calcium in the rectification of sea-water in 

 aquaria. Journal of the Marine Biological 

 Association of the United Kingdom, Vol. 18, 

 No. 1, pp. 199-200. 



Harvey. Hildebraxde Wolfe. 

 1955. The chemistry and fertility of sea- 

 waters. Cambridge University Press, viii-f 

 224 pp. 



Sverdrup, H. U., Martin W. Johnson, and 

 Richard H. Fleming. 

 1942. The oceans ; their physics, chemistry, 

 and general biology. Prentice-Hall, New 

 York. 1087 pp. 



Townsend, Charles Haskins. 



1928. The public aquarium ; its construction, 

 equipment, and management. U.S. Bureau 

 of Fisheries, Document 1045, Report of the 

 U.S. Commissioner of Fisheries for 1928 

 (Appendix VII), pp. 249-337. 



