VESSELS FOR AQUARIA. 29 



liar form, and contrived for the purpose of a marine Aqua- 

 rium, in order to keep deep-sea organisms, and for which 

 it is admirably adapted. Mr. "Warrington himself speaks 

 of it as follows : " After five years and upwards expe- 

 rience, I have now adopted an Aquarium, the form of 

 which consists in a four-sided vessel, having the back gra- 

 dually sloping upwards from the bottom at an angle of 

 fifty degrees. The chief peculiarity of this tank is, that it 

 admits light at the top only ; the back and sides arc 

 usually composed of slate." A tank of this form offers a 

 sloping side, to which we can attach rock-work, and thus 

 have a rocky shore, on which many animals like to crawl 

 up to the level of the water— the Actinia and crabs will 

 be found to be among this class. 



A word as to the cement used in the construction of 

 tanks. If the reader intends to manufacture his own (which 

 I do not recommend him to attempt, without lie has con- 

 siderable mechanical knowledge), let him, on no account, 

 use a cement containing either lead or lime, as they will 

 both dissolve in the water, and so make the tank leak • 

 and, also, they both, and especially the first of them, will 

 contaminate the water and render it absolutely poisonous 

 to the fish ; for this reason, Roman or Portland cement is 

 objectionable, as is also a cement often used by makers of 

 tanks, at least in England, and which consists of a prepa- 

 ration containing white lead. It is true that I have used 

 a tank put together with white lead, but it was carefully 

 covered with other cement, and employed for fresh water 

 only, sea water being more apt to dissolve out deleterious 

 substances from the cement. 



