170 G. F. Becker—Temperature and Glaciation. 
by topographical conditions, ete.. The higher the temperature 
of any locality, however, the more rapidly the thermometer is 
found to fall as neighboring mountains are ascended. e rate 
? 
that it does not extend over the snow belt. If so, the diminu- 
more powerful during the warm period than at the later date, 
and consequently ice and snow exposed to the sunshine 
would melt more rapidly. Neither would the conditions at 
sea level be the same. Not merely would more heat be em- 
ployed in evaporating water from the ocean during the 
warmer period, but the temperature of the ocean itself would 
be increased, especially near the surface, but also throughout 
the whole depth of shallow seas. As is well known, the rate 
of evaporation depends primarily upon the temperature of the 
surface of the water, and it follows immediately from the for- 
mulas which state the observed relations between temperature 
and tension of aqueous vapor, that the more intense the radia- 
tion from the sun, the greater will be the proportion of the 
heat employed in the evaporation of water. Appeal to obser- 
vation shows that the operation of this law is not substantially 
obstructed by the action of any other of a contrary tendency. 
The heat received from the sun upon a square mile of the 
earth’s surface, in latitude 45°, allowing for the absorption of 
the atmosphere, must be somewhat more than one half of the 
amount received upon an equal area at the equator, while the 
average rainfall of latitude 45° is only one-third of that at the 
equator. The rate of evaporation of still water in the two 
* See Loomis’s Meteorology, p. 40; Report of Chief Signal Officer, 1876, p. 348; 
and Professional papers Signal Service, I, Isothermal Lines of the U. 8. 
