354 The Scottish Naturalist. 



twenty-four hours ; this supply, it is expected, will be got 

 from the Rothesay Water Company The turbine-engine is 

 being adopted by the Rothesay Aquarium Company, as it is 

 thought to be the most economical method of effecting the con- 

 stant motion required day and night, summer and winter. Its 

 advantages are that it requires no coals, very little attention, 

 and that the only expense worth mentioning is the rates paid ' 

 for the supply of the town's water to propel it. 



Some of the Aquaria in this country, and on the continent, 

 are worked by steam power, which is very expensive, for be- 

 sides the wages of an attendant day and night, there is a great 

 consumption of coals, which adds considerably to the yearly 

 expenditure. The Avater is taken out of the reservoirs by means 

 of pumps, which are worked by the engines — the pumps being 

 made of vulcanite. 



It is generally supposed by persons who are not acquainted 

 with the principle upon which aquaria are constructed, and 

 animal-life sustained, that they must have a constant communi- 

 cation with the sea, with an inlet, and an outlet thereto. How- 

 ever, this is not so, for if there was any connection with the sea, 

 the animals would constantly be dying, and simply because, if 

 such were the case, there would of necessity be often recurring 

 changes in the temperature of the sea-water, and the animals being 

 in captivity, would be unable to adapt themselves to those con- 

 ditions which are most congenial to their existence, and which 

 the wide ocean affords them. 



Thus for example, water circulating from the sea in summer 

 would be too hot, while that during winter would be too cold. 

 The fish and other animals in the aquarium being unable to de- 

 scend to that depth which the fathomless ocean affords them 

 in their natural state of existence — would most assuredly die. 



In order, therefore, to carry out successfully the maintenance 

 of animal life in an aquarium, several conditions must be 

 observed, and the most important of these is, that the water 

 must be kept in a perfectly respirable condition, by being 

 brought into constant contact with the atmospheric air by means of 

 machinery, and to ensure that there shall be no interruption to 

 the constant movement of the water two engines are put up 

 alongside of each other and connected with the pumps, so that 

 if one engine were to get in any way disabled the other could be 

 used. The stoppage of the circulation of the water even for a few 

 hours would kill most, if not all the animals, in the aquarium. 



