Tlie Lazvs of Climatic Evolution. — Manson. 55 
to be in the first era of climatic evolution. The cloud sphere 
presents a surface of high albedo, and the heat from it is of 
about that intensity which we should receive by the reflec- 
tion of solar energy.* 
The Earth, a nmch smaller mass, has passed through the 
first era of climatic evolution, and has reached the earlier 
epoch of the second era; during this epoch glacial conditions 
are being removed and surface temperatures are slowly ris- 
^ ing. Since the rays of the violet end of the spectrum are most 
easily trapped, the Earth must reflect light in which red rays 
predominate, and it has a low albedo. 
Mars, smaller and more distant from the sun than the 
Earth, has apparently reached a still further stage of climatic 
evolution. Polar snow caps form in winter and melt ofT in 
summer,f thus indicating milder polar conditions than pre- 
vail within our polar circles. The albedo of Mars is 
low, and solar energy reflected from its surface is 
deficient in violet rays, thus showing that the atmos- 
phere of Mars, like that of the Earth, most readily traps the 
rays of the violet end of the spectrum. Thus IN'Iars is ap- 
parently in a condition towards which the climatic evolution, 
now in progress upon the Earth, is tending. 
Conclusions. The author therefore holds: (i) that the 
present zonal distribution of climates is gradually increasing 
in temperature and extent; (2) that the rise in temperature 
is due to the trapping of solar heat by the lower layers of the 
atmosphei;e; (3) that this rise in temperature was inaugu- 
rated at the culmination of the Ice age in tropical latitudes, 
and that it must be gradually checked by a denser cloud for- 
mation as the surface temperatures of the oceans are raised; J 
(4) that the Ice age was unique in the climatic history of the 
earth, and the result of the laws previously cited; (5) that 
preceding climates were independent of latitude and were 
♦Young's General Astronomy. 
tDr. E. E. Barnard, Popular Astronomy, No, 20, 1895. 
See also Young's General Astronomy, p. 2)2,1. 
JTlie equatorial cloud ring is possibly the nucleus of a more ex- 
tended ring which will protect a greater area from noon and afternoon 
exposure to direct solar energy. As evaporation was reduced to a 
minimum at the cuhnination of the Ice age. cloud formation and pre- 
cipitation, being direct functions, were likewise at a minimum and this 
ring was then probably of less extent. 
