TROPICAL AQUARIUM FISHES 107 



pedient. After hole is cut in slate, pour in lead or tin. When the metal 

 is poured, use a form made of putty so that the surface of metal will come 

 as high as the sand. The object in using the inverted pan is to have 

 the heating surface come just above the sand. Then the heat is the most 

 efficient as well as fairly diffused and does not interfere with the roots of 

 plants. The objections to this type are that the aquarium has to be raised 

 and that there is an occasional drip of condensed water caused by com- 

 bustion. The best flame to use is a small gas Bunsen burner. They may 

 be had of some scientific apparatus concerns or dealers in German 

 aquarium supplies. These dealers also handle a rather good all-glass 

 aquarium for heating by lamp, and which does not need to be raised. 

 There is, however, the eternal liability of cracking. All-glass aquaria at 

 best are liable to crack, and particularly when unevenly heated. In the 

 German catalogs and aquarium publications will be found numberless 

 heating devices, but after trying many of them and inventing some de- 

 fective ones himself, the author finds those described here the most 

 practical. Smells are caused by chilling the flame before combustion is 

 complete. No more than the tip of flame should be allowed to touch the 

 heating surface. Even this is not necessary in system shown in Fig. 7(i. 



Heat Control. In a room where there are violent changes of tem- 

 perature, particularly when these dip to the cold side, it is desirable to 

 have some means of heat control. To start in the simplest way first, an 

 aquarium may be kept noticeably warmer over night by covering with a 

 thick blanket, quilt or any warm fabric. If near a window the curtain 

 should be pulled completely down. Another help for any aquarium near 

 a window is to have a sheet of glass standing on the base and leaning 

 against the top of the aquarium. This sheds much of the cold air which 

 constantly falls from a window in cold weather. 



Tropical aquaria may be kept at a satisfactory temperature standing 

 on a hot-water radiator, the heating result not being so extreme as mi^ht 

 be supposed. 



The most satisfactory means of controlling temperature is to heat by 

 gas and use a gas thermostat to control gas flow. See Fig. 7%. This is 

 placed either in the water or tightly against the outside of the aquarium 

 and insulated from the influence of surrounding air by plenty of wool or 

 cotton batting. It contains a large body of mercury over w^hich the gas 

 passes through a small space. As the water rises in temperature, the 

 mercury expands and so reduces the gas supply, and v\ce versa. It is a 

 very ingenious and eflFective device and may be obtained from makers of 

 scientific glassware at small cost. Those selling them are glad to give 

 instructions regarding regulation, etc. The Arthur H. Thomas Company, 

 of Philadelphia, are specialists in this line. With this equipment in oper- 



