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THE POPULAR SCIENCE MONTHLY 



creasing the under light there are mirrors (s) at an angle of 45° be- 

 neath the aquaria. To dispense with these in over lighting a black 

 paper is shoved under the aquarium. Cave animals and fungi are bred 

 and observations made upon etiolated plants and regeneration against 

 the exhalations of various crystals. Through a trap door iron steps 

 descend into a dark vaulted cemented cellar room which is used as a 

 cave. The air is saturated with moisture by water standing on the 

 floor and the temperature is maintained at 12° C. 



For all of the purposes of the institution a reliable heating plant is 

 necessary. A central low pressure steam boiler furnishes rather con- 



Fig. 11. Dark Rooms from the Corridor. 



stant warmth for the main building, with a warm water system for the 

 glass houses. Small thermostats, which can be exactly regulated, main- 

 tain the desired temperature of the different rooms. The northeast 

 half of the building is kept at the ordinary room temperature (17° C), 

 while the southwest half is warmer and includes seven rooms. In a 

 glazed compartment (Fig. 13) is the highest temperature (37° C), 

 next the portion of the same room separated by the glass partition 

 (27° C), then the warm glass house and the warm corridors for ter- 

 raria and aquaria (20°-25° C). A large basin is warmed in winter by 

 a tinned tube kept at 10°-12° C. 



The Vienna institution for experimental biology is a pioneer in the 

 use of the carbonic-acid cooling machine for maintaining a cold en- 



