64 THE SEA SHOBE 



add that these practically disappear when one is prepared to devote 

 a short time at regular intervals in order to see that the process of 

 aeration is properly carried out. 



Some recommend the occasional injection of air by a syringe 

 as one means of aerating the water ; but, although this may be all 

 very well as a temporary purifier of the slightly tainted aquarium, 

 it is hardly suitable as a means of maintaining a good, healthy 

 condition. It must be remembered that oxygen gas the gas of 

 the atmosphere so essential to animal life is only very slightly 

 soluble in water. By this we mean not only that water dissolves 

 oxygen very slowly, but also that it can never hold a large supply 

 of the gas at any one time. This being the case, it is clear that 

 the use of a syringe for a short time, though it discharges an 

 enormous total volume of air into the water, will result in the 

 actual solution of onty a small quantity. No method of aeration is 

 perfect that allows the admission of air for a short time only at com- 

 paratively long intervals ; the most perfect system is that in which 

 air is slowly but continuously passed into solution. 



Since air is slightly soluble in water, it is clear that it must be 

 continuously passing into any body of water that has its surface 

 freely exposed to it ; hence a wide and shallow aquarium is much 

 more likely to keep in good order than one that is narrower and 

 deeper. But, with marine aquaria, the simple absorption from the 

 air at the surface is not in itself sufficient, as a rule, to maintain a 

 healthy condition. Yet it will be advisable to remember this matter 

 when constructing a tank for marine life. 



One of the prettiest, and certainly one of the most effectual, 

 methods of supplying air to an aquarium is by means of a small 

 fountain with a very fine spray. The water need seldom be 

 changed, but the fountain may be fed by water from the aquarium, 

 and as the fine spray passes through the air it will absorb oxygen 

 and carry it in solution to the tank. 



The accompanying diagram illustrates the manner in which 

 this can be accomplished. The aquarium (A) is supplied with an 

 outlet (o) about an inch from the top by means of which the water 

 is prevented from overflowing, and the outlet pipe leads to a vessel 

 (v) of considerable capacity which, for the sake of convenience and 

 appearance, may be concealed beneath the table on which the 

 aquarium stands. Some feet above the level of the aquarium is 

 another vessel (c), supported on a shelf, having about the same 

 capacity as v, and supplied with a small compo pipe that passes 



