RAIN AND SNOW 



89 



be illustrated in a simple way by putting a sup- 

 posititious case in which I shall use the figures 

 of Dr. Eobert Mann. 



At 32 Fahrenheit a cubic foot of air can 

 hold or carry 2.37 grains of vapor in invisible 

 form. It is then said to have reached its " dew- 

 point." If into that cubic foot of air 2.38 grains 

 of vapor were injected, the result would be one- 

 hundredth of a grain of condensed mist or 

 cloud. At a temperature of 60 each cubic foot 

 of air can carry 5.87 grains of invisible vapor ; 

 at 80 each cubic foot can carry 10.81 grains. 

 Consequently, if at any time or for any reason a 

 saturated air at a temperature of 80 were sud- 

 denly chilled down to 60, nearly 5 grains of sur- 

 plus vapor would be condensed out of each 

 aerial cubic foot in the form of tiny droplets of 

 rain. 



If at a temperature of 32, the freezing 

 point, similar conditions prevailed that is, if 

 a saturated air at 32 were suddenly chilled 

 down to zero a similar surplus quantity of 

 vapor would be condensed in the form of crys- 

 tallized spicnles of ice or snow. A more violent 

 reduction in the temperature of a saturated 

 cloud say from 100 down to 60 would pro- 

 duce more vapor than the cloud could hold, 



