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. Robert Mann. 
At 32° Vahrenheit 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.” Ifinto 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. Ata 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 
acrial 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 spicules 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, 
The dew- 
point and 
condensa- 
tion. 
