TESTING THE THERMOMETER 241 



at the level of the centers of the eggs; the other is hung directly 

 above the eggs, with the bulb as close to the eggs as is practic- 

 able, but not touching them. See Fig. 151. It is a mistake to 

 have the thermometer in contact with the eggs, because the 

 temperature will vary with the vitality of the egg touched by it. 

 Touching good eggs it will be high; next to weak or dead germs it 

 will be low, thus never registering the real temperature of the 

 egg chamber. 



Unless there is a very good reason for changing the position of 

 the thermometer, it should be used in strict accordance with the 

 manufacturer's directions. In some egg chambers a difference 

 of an inch in the height of the bulb will make a difference of a 

 degree in the temperature. 



Testing Thermometer. — It is a good plan to test the ther- 

 mometer once a year, even with a new machine. This can be 

 done by comparing it with a clinical thermometer, which has 

 about the same scale and range; place both instruments in warm 

 water, heated to about 103 degrees, which should be stirred, and 

 the bulbs kept in about the same position. Or a thermometer 

 can be certified by an optical goods store or a reliable drug store. 



The thermometer is placed near the front of the egg chamber 

 so that it can be easily read without opening the door to the 

 machine. Even so some thermometers are particularly difficult 

 to read, and it is surprising that so little improvement has been 

 made in this respect. An electric flash lamp is very helpful in 

 reading a thermometer. By all means learn to read the ther- 

 mometer without opening the door; to so do will cause the tem- 

 perature to fall. 



Set Machine Level. — ^The incubator should be set up level by 

 all means. Heat rises to the highest point, and if the machine 

 is not plumb, one part of the egg chamber will be warmer than 

 the other. Do not guess at the level of the machine, but test it 

 with a spirit level, both ways, for length, and breadth, and cor- 

 rect any irregularity with thin blocks of wood under the legs of 

 the machine. 



Some manufacturers are careless about the fit of the door, or 

 16 



