HYPOTHESES BEARING ON CLIMATIC CHANGES 681 
ment would produce the warm climate of the Tertiary. He 
arrives at the conclusion that the removal of 38 to 45 per cent. 
of the present carbon dioxide would bring on glaciation and that 
an increase of 2.5 or 3 times its value would produce the mild 
temperatures of the Tertiary times. He quotes the opinion of 
Professor Hégbom in support of the competency of earth changes 
to produce this depletion, and also the competency of the interior 
and other sources to re-supply the impoverished atmosphere. 
He, therefore, carries the suggestion of Tyndall and others a very 
notable step in advance, and, what is especially important, has 
given it quantitative expression on the basis of deductions from 
observed data. He does not, however, postulate the conditions 
which control the enrichment and depletion of the atmosphere 
which has been the essential endeavor of this paper.’ 
But we do not meet geological demands when we simply 
offer general explanations of climatic changes. Our theories 
must ultimately be found to fit the precise phenomena. How 
are we to explain the profound glacial oscillations? Here is 
where existing hypotheses are put to the stress and our atmos- 
pheric hypothesis seems at first thought even less adaptable to 
the phenomena than most others. If we could deny that the 
oscillations were profound, as some do, it would be convenient. 
But I fear we cannot. We may appeal to variations of atmos- 
pheric supply, to the precession of the equinoxes, etc., but field 
experience leads me to doubt whether these will fully fit the 
phenomena, though they must doubtless be reckoned as factors. 
I have endeavored to follow out the doctrine of atmospheric 
gain and loss on its own lines, and although the studies are 
incomplete, the results are at least encouraging. I seem to find 
a rhythmical action that may in part explain the glacial oscilla- 
tions. To do it justice it should have elaborate and careful 
statement, but I can here only suggest its nature in bald outline 
*T may here remark that the main features of the ideas herein advanced were 
entertained and expressed to my students some time before I saw Dr. Arrhenius’ 
important paper, but I fear I might not have felt justified in giving them a more pub- 
lic statement but for the encouragement of his weighty opinion on the vital point of 
quantitative sufficiency. 
