38 CONSTRUCTIVE BEEKEEPING 



to moisture in the air, will be necessary to comprehend wher>e 

 this water vapor comes from. The amount of water vapor in the 

 atmosphere is ascertained by using two tested thermometers. 

 One, called the dry bulb, is exposed and the temperature [noted. 

 The other one has a cloth covering the bulb. This cloth is mois- 

 tened and the thermometer whirled in the air for a short time, 

 and the temperature noted. Then by subtracting the tempera- 

 ture of the wet bulb from that of the dry bulb, we have a basis for 

 computing the dewpoint, and from this the relative humidity. 

 Knowing the tmeperature of the dewpoint and the amount of 

 water vapor that saturates the air at that temperature, we have 

 the absolute humidity. Divide the absolute humidity of the dew- 

 point by the absolute humidity of the dry bulb temperature and 

 you have the relative humidity. 



Air can be supersaturated; that is it can contain water in 

 excess of that which saturates it at its temperature, but this 

 excess water is held in the air in globules of water and is known 

 as fog or clouds. The excess water has given up all its gaseo_us 

 properties and is not subject to the same laws as the water vapor 

 cf the air. 



The gaseous vapor of the air is controlled by the same laws, 

 in regard to its expansion and contraction as air. It is well 

 known that if a chamber, in which the air is rairif ied, is opened, 

 the air rushes in from the outside until the outside and inside 

 air have the same density. 



Water vapor does not rush into a hive, where the hive air is 

 relatively dry and a small opening is maintained, but is slowly 

 forced in until its tention at hive temperature equals the tention 

 of the outside vapor at outside temperature. Because of this slow 

 movement of water vapor, when its tention inside the hive is 

 greater than on the outside it condenses on the inner walls, or is 

 transformed into fog, which then looses the expansive power of 

 a gas and is retained in the hive. 



Disturbance inside the hive which causes the bees to raise 

 the temperature of the hive air, with its then greater capacity 

 for moisture, or a fall of temperature or raise of relative hu- 



