3754 The Zoologist — November, 1873. 



The great bulk of water in the ocean being then in its " dark 

 unfathomed caves," the plan of keeping it dark in an aquarinra is 

 obviously little more than a direct obedience to the teachings of 

 Nature, and there is little necessity for explaining the principles 

 which require, or the circumstances which accompany, profound 

 darkness. Sea-water constantly exposed to light is apt to become 

 opaque and of a greenish brown colour — a very serious evil in a 

 public aquarium. The darkened tank extends under the floor of 

 the aquarium from end to end (/. e. beneath g, g, f, &c., in the plan) 

 and also under the compartments marked 9 and 10. It is no part 

 of Mr. Lloyd's design to change or renew this vast bulk of water, 

 but it will become necessary to add from time to time a portion of 

 distilled fresh water to compensate for the waste which must in- 

 evitably result from evaporation, leakage of pipes, or breakage of 

 glass, this last being a calamity to which all such establishments 

 are unfortunately subject. 



Keeping the plan still in hand, the compartments or pigeon-holes, 

 representing tanks, are numbered 39 to 60, 1 to 18 a, 38 to 28, and 

 27 to 19, are also filled with water, and contain altogether no less 

 than 20,000 gallons, in which the living objects of the aquarium 

 constantly reside, and all of which are lighted from above, nineteen 

 of them having in addition one side (that fronting the area, g g) of 

 plate-glass, by which means additional light can penetrate the 

 water and illuminate the objects living therein. Thus the entire 

 quantity of water is 120,000 gallons, of which five-sixths is in the 

 dark and one-sixth in the light. This large quantity of water is 

 kept in constant circulation ; a steam engine of three-horse power 

 (m) and one of Forbes' patent vulcanite pumps (n) work day and 

 night to raise water from the dark reservoir (g g f) and discharge it 

 into the light reservoirs 9 and 10, at the rate of from 5000 to 7000 

 gallons per hour. 



This engine and pump are necessarily in duplicate, because if 

 either should break down through any unforeseen casualty, the 

 motion of the water would be arrested and the lives of the prisoners 

 jeopardized; indeed, so dependent are these on this sea-like move- 

 ment of the water, that the stoppage of a pump for a single hour has 

 produced visible effects on their health and spirits. These pumps 

 and engines necessitate the employment of three engine-men, and 

 these relieve each other every eight hours, so that one is always 

 on duty. The exigencies of the animals also necessitate the 



