C. EL. Dutton—Lffect of a warmer Climate upon Glaciers. 3 
precipitation is necessarily all rain; for the precipitate must 
take the temperature of the menstruum. If the two limiting 
temperatures are both below zero the entire precipitation is 
one limit is above and the other below zero a part o 
the precipitation is rain and the other part snow. From this it 
follows that whatever moisture air may contain in excess of the 
quantity which is necessary to saturate it at zero can fall only as 
rain; and the only available supply which can form snow ts a 
portion of the moisture which is required to saturate air at zero. 
4.) To avoid circumlocution it will be considered, unless dis- 
tinctly specified otherwise, that the air is saturated with mois- 
ture at all temperatures. The amount of precipitation is an 
increasing but complicated function of the amount of fall of 
temperature, Without such a fall there can be no precipita- 
tion. But equal falls do not give the same amount of precipi- 
tation in different parts of the temperature scale. Thus a fall 
from 20° to 19° precipitates much more than a fall from 10° to 
9°, and this much more than from 0° to-1°. The exact form 
average, and these averages are susceptible of perfectly rational 
' €Xpreassion. Suppose we had thrice-daily observations for a 
thousand years of all the meteorological conditiong of a locality. 
The average of these observations would, in respect to eac 
factor, give perfectly definite values and relations, Let us 
