6 



BULLETIN 951, U. S. DEPAETMENT OF AGRICULTURE. 



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apparatus for the first incubating compartment was designed and 

 for the most part constructed in the bureau. Tlie temperature-con- 

 trol system for the 

 other compartment 

 consists largely of 

 assembled com- 

 mercial apparatus. 

 The heating units 

 consist of resistance 

 tubes or coils fed 

 from a 220 -volt, 

 direct-current line. 

 The electric current 

 is turned on and off 

 the resistance units 

 by means of a ther- 

 mostat in the incu- 

 bator compartment. 

 The thermostat is 

 adjusted to turn 

 the electric current 

 on and off with a 

 variation of room 

 temperature of 1° 

 C, that is, 0.5° 

 above and 0.5° 

 below the optimum. 

 It is possible to ad- 

 just the thermostat 

 to turn the electric 

 current on and off 

 between much closer 

 limits, but the 

 limits of 0.5° above 

 and 0.5° below the 

 optimum tempera- 

 ture give satisfac- 

 tory results, and 

 the frequency of 

 operation and hence 

 the wear on the 

 controlling appara- 

 tus are decreased. 

 The temperature- 

 control equipment 



