feelations of the Atmosphere. 359 
Ebelmen, and others after him, have deduced with regard to 
the temperature of the earth’s surface in former geological 
prneds, would seem, at first sight, to be invalidated. Tyndall, 
owever, in 1861, from a consideration of the great power of 
absorbing heat possessed alike by aqueous vapor and by cer- 
tain gases, such as carbonic dioxide, and the cousequent effects 
of small quantities of these in the atmosphere on terrestrial 
radiation, and thus on climate, was led to remark, ‘it is not 
therefore necessary to assume alterations in the density and 
eat being preserved to the earth in different times; a slight 
Which, in past geological ages, has been, by chemical processes 
at the surface of and other worlds, abstracted from 
the universal medium, may not have sufficed to diminish by 
s 
it in allits bearings would require a volume. The climatic 
influences of a denser terrestrial atmosphere, or one of greater 
Ebelmen, E. B, Hunt and Duncan, and, as we have seen, the 
* Tyndall, Bakerian lecture for 1861; L., B. & D. Phil. Mag., Oct., 1861, and 
Hunt, Uhem. and Geol. Essays, pp. 42 and 46. 
