176 Tlie American Geologist. Soptomber, is99 
cates that there is a positive difference between the rates o! 
receipt and loss of solar energy; or in other words that Mars, 
like the earth, is a heat-trapping body, and that either its sur- 
face temperatures are yet gradually rising; or, that its mean 
surface temperatures are practically constant, and the de- 
ficiency of solar energy represented by the absence of the blue 
rays is used in maintaining these constant conditions, and in 
work upon the planet's surface. 
The third cause — the factor time — is necessarily greater 
than' the corresponding factor in the case of the earth; for 
Mars, having a mass less than one-ninth that of the earth, 
must have lost its internal heat at an earlier period, and there- 
fore became a heat-gathering body at an earlier period than 
the earth. 
Thus three of the principal factors influencing climate are 
positively and probably cumulative in their effects for long 
periods of time. It is therefore reasonable to infer that similar 
climatic conditions must in time be established upon any 
planet having a heat-trapping atmosphere, and that the milder 
conditions indicated by the annual melting off of the polar 
caps of the planet Mars are those toward which the progress- 
ive rise of temperatures since the culmination of the Ice age 
indicate for the future of the earth.* 
Chapter VIII. 
Tlie Cosmic Laws of Climatic Evolution. 
The writer has endeavored to show that the glaciation of a 
planet is the direct and necessary result of known laws, and 
the culmination of a series of uniform climates controlled by 
the resident internal heat of the planet; that upon the close of 
this series solar energy gradually established its control, and 
*The observations of Dr. Barnard at the Lick Observatory corrobo- 
rate these conclusions. Dr. Barnard says of the results of an ex- 
tended series of observations of the south polar cap, in 1892-4: "That 
the cap steadily diminishes after the summer solstice, showin<^ that, as 
on the earth, the temperatures of Mars continues^ to rise after the 
summer solstice — the maximum temperature occurring several months 
after the maximum of solar heat has been received, thus indicating a 
heat storing atmosphere. This fact is in good agreement with Dr. Man- 
son's interesting paper on the climate of Mars, in Popular Astronomy 
for April." 
Popular i\stronomy No. 20, 1895. 
