TEMPERATURE OF WATER. 155 



temperature are both too powerful, we cannot expect 

 other than the utmost disorder and zoological anarchy. 

 Mr. W. R. Hughes, speaking on this point, says, " It 

 is certain that light is the primary question to be con- 

 sidered in relation to aquaria. The presence of an 

 uninterrupted volume, combined with a high rate of 

 temperature, may in a few days convert an aquarium, 

 which was in an efficient condition of health and 

 beauty of the inhabitants, into a decomposing mass." 

 Moreover, so auxiliary is the effect of light or heat 

 respectively, that it is necessary to reduce the light 

 admitted to a tank when the temperature is rising. 

 Fifty degrees, or from that to fifty-five is about 

 the highest heat which should be allowed ; and the 

 light should be toned down as the water reaches the 

 higher point. Mr. Lloyd insists with great emphasis 

 upon the necessity of keeping the temperature low, 

 and this, he contends, can only be effectively done by 

 having a store of water several times the bulk of that 

 in the show tank. 



It is evident that, do what we will, some of the sea 

 water cannot fail to be evaporated during the process 

 of fountain or syphon aeration ; or even when the 

 surface only is exposed to the air. But it should be 

 remembered that what is thus lost by evaporation is 

 only the fresh part of the water. The salts are 

 left behind we cannot evaporate them ; and so they 

 tend to render the remaining water all the salter and 

 denser. Hence there is an immediate necessity for 



