94 
Psyche 
[Vol. 92 
Fig. I. Linear temperature gradient apparatus, semi-schematic. A. View from 
above of gradient chamber and associated equipment. B. View of cross section 
through Plexiglas test chamber. Shaded areas are polystyrene foam insulation. I, 
strip heaters; 2, valve for controller flow rate of coolant; 3, cold water input conduit; 
4, cold water return conduit; 5, wooden housing for chamber and closely associated 
parts; 6, Plexiglas test chamber; 7, cold water compartment for cooling aluminum 
channel; 8, aluminum channel for housing Plexiglas test chamber; 9, introduction 
ports for test animals; 10, dead air space; 11, lid of test chamber; 12, “condensate 
wipers”, magnets; 13, porous substrate; 14, space for humidity controlling substan- 
ces; see text for further details. 
one in 1.5 cm dead air space, and one below), which were used as 
“condensate wipers” (Fig. IB- 12). By adjusting the two temperature 
controllers and the flow rate of the coolant, a linear temperature 
gradient between 15° and 35° C was obtained. A constant 22 ± 1°C 
was obtained by turning off both strip heaters and the water bath 
pump. During the experiments two humidities were employed. A 
saturated atmosphere was obtained by placing wet paper toweling 
beneath the substrate in the test chamber (Fig. IB-14), and 0% R. 
H. was obtained by the use of Drierite (CaS0 4 ). 
