Page:Popular Science Monthly Volume 78.djvu/604

594 the under light there are mirrors (s) at an angle of 45° beneath 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 constant

warmth for the main building, with a warm water system for the glass houses. Small thermostats, which can be exactly regulated, maintain 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 terraria 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