31Q POULTRY BREEDING AND MANAGEMENT 



water evaporates on the bulb of the thermometer the tem- 

 perature is lowered. The rate of cooling depends upon the 

 rate of evaporation. If the evaporation is great or rapid 

 the temperature is lower; if the evaporation is less the 

 temperature rises. The rate of evaporation is influenced 

 by the amount of moisture in the air surrounding the ther- 

 mometer. The reason for this is that the air takes up 

 moisture fast or slow as it approaches or departs from the 

 point of saturation. "When the wet and dry bulbs have 

 the same temperature the point of saturation has been 

 reached and instead of being taken up by the air, moisture 

 is given off; this is what causes rain. The drier the air, 

 therefore, in the machine the greater its thirst for moisture, 

 therefore the more rapid the evaporation of moisture from 

 the wick on the bulb the greater the consequent cooling of 

 the bulb. The drier the machine the more moisture will 

 evaporate on the bulb and the lower the temperature of 

 the wet bulb will be. The more moisture in the air the 

 higher the temperature of the wet bulb will read. 



What is the Best Wet Bulb Temperature for Hatching? 

 In machines with no supplied moisture there was an 

 average wet bulb temperature of 84 to 85 degrees. Machines 

 of the same make, with a tray of wet sand covering half 

 the floor of the egg chamber, averaged about 88 degrees; 

 and in others with a tray of wet sand covering the entire 

 bottom of the machine the temperature was 90 to 91 degrees. 



As reported in Oregon Bulletin 100: "An average wet 

 bulb temperature of 87.6 gave 32.6% better hatches than 

 one of 84.5% and slightly better than one of 91%." 



Later experiments at the same station confirm these re- 

 sults. The importance of moisture is strongly indicated. 

 The efficiency of the particular incubator used was in- 

 creased over 30% by using an amount of moisture that 

 maintained a wet bulb temperature of 88 degrees instead 



