692 



THE POPULAR SCIENCE MONTHLY. 



be covered with a layer of sand from one to two inches thick, upon 

 the top of which should be placed a few pebbles, in patches. For ma- 

 rine aquaria, the sand must be procured from the sea-beach, or a river- 

 side, below the tide-mark, and, for those of fresh water, from the bed 

 of a brook or running stream, and, in either case, it must be thoroughly- 

 washed, to free it from impurities. Rock-work may be built upon the 

 sand, to form caves and grottoes, but there should not be any hiding- 

 places for impurities to collect in. A pleasing effect is secured by 

 building the rock-work above the surface of the water, and making a 

 small hollow in the top, where a fern may be jjlanted. The rock should 

 be taken from the sea, or the brook, according as it is wanted for the 

 marine or fresh-water aquarium, the object being to make the artificial 

 home of the animals as much as possible like their natural one. In 

 constructing the rock-work, Portland cement should be used, and it 

 should be allowed to harden before the water is poured into the tank. 

 The water should be poured off several times, until it remains quite 

 clean, and the greatest care should be taken to prevent the addition 

 of impurities with any object. The plants must be stuck into the sand 

 with a pebble tied to the roots of each to hold it in position, and they 

 should be arranged to produce a pleasing effect, as individual taste 

 may dictate. After the plants have taken root, the animals may be 

 added. If both forms of life be present in proper proportions, there 

 will be no necessity for change or disturbance of the water, but, if they 

 be not, artificial aeration will be required. When this is needed, the 



Fig. 3. 



FREeH-WATER AqUARIUM. 



fish will repeatedly rise to the surface and stick their noses out to catch 

 a breath of oxygen. Aeration may be effected in lifting the water by 

 cupsful, and allowing it to run back gradually from a point two or 

 three feet above. This process should be continued for a half-hour or 

 more at a time, once or twice a day. The ordinary level of the water 

 should be indicated by a mark on the glass-front, so that loss from 

 evaporation can be detected and supplied. Great care must be taken 

 to secure uniformity of temperature, between 45° and 65° Fahr. For 

 this purpose an east window should be chosen where the sun can be 



