5702 The Aquarium. 



provision for the removal of decaying animal matter, and converting it 

 into food for both fish and man. 



LIGHT. 



It is most probable that the greater amount of failures with the 

 aquarium have arisen from the want of a proper adjustment of this 

 most important agent, the tendency being generally to afford as much 

 sun's light as possible ; but on consideration it will be found that this 

 is an erroneous impression. When the rays of light strike the glassy 

 surface of the water, the greater part of them are reflected, and those 

 which permeate are refracted and twisted in various directions by the 

 currents of the water; and where the depth is considerable it would 

 be few rays which would penetrate to the bottom ; but let the surface 

 become ruffled by the passing wind, and it is little light that can be 

 transmitted; and when this same disturbing cause lashes into waves 

 and foam, not a ray can pass, and all below must be dark as night. 

 Too much light should therefore be avoided, and the direct action of 

 the sun prevented, by means of blinds, stipling, or the like. It is a 

 great desideratum to preserve the growth of the lovely red Algae in all 

 their natural beauty, and prevent their becoming covered with a pa- 

 rasitic grow r th of green or brown-coloured plants ; this can be effected 

 by modifying the light which illuminates the aquarium, by the inter- 

 vention of a blue medium, either of stained glass, of tinted varnish, 

 coloured blinds, &c. The tint should be that of the deep sea, a blue 

 free from pink, and having a tendency rather to a green hue. This 

 modified light affects also the health of those creatures which are 

 confined to shallow waters, so that a selection of the inhabitants 

 must be made. 



HEAT. 



The proper control of this agent is also most material to the well- 

 being of these tanks ; for experience has proved that an increase or 

 diminution of temperature beyond certain limits acts most fatally on 

 many of the creatures usually kept. These limits appear to be from 

 45° to 75° Fahrenheit. The mean temperature of the ocean is estimated 

 to be about 56°; and this does not vary more than 12° throughout the 

 varying seasons of the year, showing the extreme limits to be from 44° 

 to 68°. Great care should therefore be taken to afford as much pro- 

 tection as possible, by the arrangement of the rock-work, both from the 

 sun's rays by day, and the effects of radiation at night, as, from the 



