66 THE SEA SHORE 



have both been filled with sea water. The fine jet from the pipe 

 plays into the air and returns with a supply of oxygen to the 

 aquarium, while the excess above the level of o passes into the 

 concealed vessel below the table. If the two vessels are as large 

 as we recommend, and the jet a very fine one, the fountain may 

 continue to play for hours before c is empty, the animals of the 

 tank being favoured all this time with a continuous supply of air. 

 And when the supply from above is exhausted, the contents of the 

 bottom vessel are transferred to the top one, and at the same time 

 so effectually strained by the layer of muslin that no sedimentary 

 matter passes down to choke the fine jet of the fountain. One 

 great advantage this method possesses is that the living creatures 

 derive the benefit of a much larger quantity of water than the 

 aquarium alone could contain ; and thus, apart from the aerating 

 effects of the fountain, the result is the same as if a much larger 

 tank were employed. 



In our next illustration (fig. 39) we give a modified arrangement 

 based on the same principle which may commend itself by preference 

 to some of our readers. Here the supply pipe to the fountain 

 passes through a hole in the bottom of the aquarium instead of 

 into the top, and the outlet pipe is bent downward within so as to 

 form a syphon. 



Those who are acquainted with the principle of the syphon will 

 understand at once the working of such an arrangement as this. 

 Let us suppose the vessel c to be full of water, and the fountain 

 started, while the water in the aquarium stands no higher than the 

 level I. The water slowly rises until the level h of the bend of the 

 outlet tube has been reached, and during the whole of this time 

 no water escapes through the exit. As soon, however, as the latter 

 level has been attained, the water flows away into the lower vessel, 

 into which it continues to run until the lower level is reached, and 

 then the outflow ceases, not to commence again until the fountain 

 causes the water to rise to the upper level. 



From what has been said the reader will see that the total 

 quantity of water required in this instance need not exceed the 

 capacity of the aquarium ; also that each of the vessels connected 

 with water supply and waste should have a capacity equivalent to 

 the volume of water contained in the aquarium between the two 

 levels h and Z. 



The alternate rising and falling of the water produced in the 

 manner just described represents in miniature the flow and ebb 



