680 The (C3 (CLEANSE STRILION, 
formly for one hundred years.t. Animal life, however, makes 
such nearly complete returns that the permanent loss is usually 
regarded as negligible. Nevertheless it is something. In cer- 
tain stages of the world’s history it has been important, as the 
coal beds testify. The loss in the Carboniferous age has been 
held sufficient to remove a noxious excess from the early atmos- 
phere. On the same basis it might be held to cause serious deple- 
tion in the absence of the excess. It is necessary at least to 
consider whether, under the theory of a limited early atmosphere, 
conditions which restrain the animal factor of the organic cycle 
may not so far impoverish the air as to seriously affect climate. 
But this cannot be entered upon here. ‘The organic cycle is very 
sensitive and very rapid in its action. It would naturally be 
greatly influenced by the topographic conditions which were 
concerned in the supply and exhaustion of the atmosphere, and 
lend to them either its concurrent or its counteracting influ- 
ences. 
It is now a little more than fifty years since Tyndall sug- 
gested that the periods of terrestrial glaciation might be depend- 
ent upon the carbon dioxide of the atmosphere whose peculiar 
competence to retain solar heat he had demonstrated. The sug- 
gestion of the origin of glaciation through the depletion of this 
atmospheric constituent is, therefore, not at all new. It has 
been entertained by others than Tyndall. If it has failed to 
find much acceptance this has perhaps been partly from a 
doubt as to its adequacy and partly from the lack of any 
definitely assignable cause for the requisite intermittent deple- 
tion. Dr. Arrhenius has recently contributed to the subject 
a most important discussion bearing especially upon the 
former point.? By an elaborate mathematical analysis of data 
derived from Langley’s experiments he has endeavored to 
ascertain what degree of depletion of the carbon dioxide of the 
present atmosphere would bring on the conditions of Pleisto- 
cene glaciation, and, on the other hand, what degree of enrich- 
t How Crops Feed, p. 47. 
2Svente Arrhenius, Phil. Mag. S.5, Vol. XLI, No. 251, April, 1896, pp. 237-279. 
