HUMIDITY 103 



By determining the dew point as was done in Experiment 39 

 and comparing this with tables which have been prepared 

 by meteorologists from many observations, relative humidity 

 can always be approximately determined. An instrument 



STRATO-CUMULUS CLOUDS 



Typical low level clouds, indicating showers. 



for determining the relative humidity of the air is called a 

 hygrometer (Figure 50). 



To be considered moist, air must contain at least more 

 than half the amount of moisture it is capable of carrying. 

 If air contains much more than half the moisture it can carry, 

 its humidity is said to be high. When air which has a high 

 humidity is cooled it soon reaches a point of temperature 

 where it is saturated (the dew point). If the temperature 

 falls below this point, the air must deposit some of its mois- 



