ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
439 
maintaining constancy of temperature within 0’1° C. Experimentally, 
it lias been shown that a certain temperature can be maintained constant 
for days. In adjusting the stage for the certain temperature, say 37° C., 
all that is needed is to pass the main current through the coil until the 
thermometer reads 37 3 ; the screw E r, with its platinum point, is then 
turned inwards until a click of the electro-magnetic contact-breaker 
indicates that the platinum point and the mercury are in contact. The 
apparatus is now regulated for a constant temperature of 37 . In order 
to adjust the regulator for a higher temperature, say 45° C., it is only 
necessary to turn the screw Er back until the thermometer indicates the 
Fig. 104. 
Fig. 105. 
•desired temperature. The transition from a higher to a lower tempera- 
ture is effected in the simplest way by breaking the main current for a 
short time until the temperature falls to the required point ; the platinum 
point is then placed at the degree which indicates the desired tempera- 
ture. In the event of the temperature falling below the required point, 
it is only necessary to turn the screw E r slowly back ; this causes the 
temperature in the stage to rise again ; and as soon as the required 
temperature is reached, the screw is slowly turned inwards until the 
clicking of the magnet indicates the completion of the circuit. The 
apparatus is thus adjusted for a constant temperature. 
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