S. Newcomb—Some points in Climatology. 21 
Arr. [IV.—On some points in Climatology. A rejoinder to Mr. 
Oroll; by Stuon Newcoms. 
at we are concerned with is the inference that at some 
former epoch in geological history the mean temperature of the 
northern hemisphere was much lower than it is now. Assum- 
ing this as the basis of discussion, the question is, what was the 
cause of this “glacial epoch?’ To speak more accurately ; 
since we can only take the causes relatively, why was the 
ical causes, combined with elementary considerations in dec 
the motion of heat and its relation to meteorological p 
ena. His conclusion is that a great eccentricity of the earth’s 
not that Mr. Croll’s thesis was false, but that it was not proven. 
Ido not deny the possibility that, when the laws of climate 
Causa acting in this direction which has not been considered by 
Mr. Croll at all, Ex eriments on radiation, commenced with 
’, 
ulong and Petit, tend to show that N ewtons theory of ot cae 
Proportionality between temperature and radiation is not well | 
