170 Tlie American Geologist. September, i^ysi 
increase of evaporation due to rising temperature.* There is 
not now, nor has there been at any period since the culmination 
of the ice, any known source of heat, save solar energy, which 
is capable of effecting the temperature changes which have 
come about since the culmination of the Ice age. 
We must therefore conclude that this rise in the isotherm 
marking glacier ice is due primarily, if not entirely, to an ac- 
cession of solar heat. 
It has been demonstrated that at the culmination of the Ice 
age, much colder conditions existed than at present. It now 
remains to explain the conditions acting to bring about exist- 
ing climates. Upon the exhaustion of the effective remnant of 
earth heat — left in the oceans by reason of the high specific 
heat of water — the supply of vapor maintaining the cloud en- 
velope was shut off, and solar heat was permitted to reach the 
planetary surface. 
That direct solar rays are converted into obscure or dark- 
heat rays by contact with the planetary surface, and that the 
atmosphere of our planet is more transcalent, to the former than 
to the latter, has been fully demonstrated by Tyndall,f al- 
though slightly modified by subsequent investigations.;!; 
The researches of Melloni and Langley tend to show that 
there was a misconception on the part of Tyndall of the terms 
and mode of action of the heat storing power of media. The 
latter investigator employs the term radiant energy in place of 
the simpler expression heat; and expresses the trapping process 
by the phrase, selective absorption of radiant energy. 
As tlTis selective absorption is a cumulative process the re- 
sults remain the same, whether interpreted along the lines laid 
down by Tyndall's and Buff's determinations, or along those 
indicated by Melloni and Langley. Both lead to the same con- 
*At the culmination of the Ice age evaporation reached a minimum 
by reason of the lower temperature of the oceans; hence precipitation 
was also at a minimum. Since that age ocean temperatures have 
gradually risen and hence evaporation has slowly increased; the amount 
of moisture in the atmosphere, being dependent upon its temperature, 
has also increased. The aggregate amount of evaporation and the ag- 
gregate amount of precipitation must be slowly increasing and have 
the moderate limit fixed by natural laws. 
tProc. Royal Soc, Vol. XIII, p. 160, Philosophical Transactions, 
Vol. 152, p. 95; Archives des Sciences, Vol. V, p. 293. 
JLangley's Investigations on the Action of the Atmosphere on 
Solar Radiation. Mem. National Academy of Sciences, 1885-7. 
