Tlie Evolution oj Climates. — Manson. 179 
solar energy, and the snsceptibilit};. of the different portions 
of the globe to be influenced by such exposure. That these 
new conditions must inaugurate a new distribution of tem- 
peratures ranged in zones and subject to solar control. 
The necessary corollaries of these postulates are : (a) That 
a planet having water and air within the sphere of its control, 
which has not yet exhausted its internal heat, must be densely 
shrouded in clouds whose outer surface presents a high albedo. 
(b) That a planet whose internal heat has been practically 
exhausted, and which holds water and an atmosphere within 
the sphere of its control must reflect solar energy deficient in 
those rays which are most readily trapped, or selectively ab- 
sorbed by its atmosphere, and it must have a low albedo, and 
that the color of its reflected rays must be controlled by those 
least readily utilized and trapped. 
(c) That glacial conditions may exist locally during any 
period of a planet's climatic evolution provided there be re- 
gions sufficiently elevated; but that an Ice age occurs as its 
oceans are finally exhausted of their available remnant of plan- 
etary heat; that this age marks the period during which sur- 
face temperatures pass from interior to exterior control, or 
is the transition period of its climatic evolution, and is unique 
(d) There are two great eras in the climatic evolution of 
a planet; ist, the era during which its internal heat controls 
its surface temperatures, and solar heat acts principally as 5« 
conservator of interior heat; 2nd, the era of solar control of 
climates. The former being an era of gradually decreasing 
temperatures of uniform distribution at sea level; and the 
latter an era of gradually rising temperatures of a zonal dis- 
tribution. The two eras, so far as land areas are concerned, 
must be separated by an Ice age. The differences in the 
specific heat of land, and that of water, permits the land areas 
to cool first. The precipitation of snow upon them nuist there- 
fore have been cumulative, until the oceans were reduced to 
about the point of maximum density. 
It is reasonably certain that glacial conditions were first 
removed from equatorial regions, and that maximum giacia- 
tion of land areas in temperate latitudes may have occurred 
subsequent to the inauguration of solar control over ecpiatorial 
latitudes, and that polar glaciations may have reached their 
