THE 
LONDON, EDINBURGH, and DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FIFTH SERIES.] 
OCTOBER 1883. 
XXXVII. On some Controverted Points in Geological Clima- 
tology ; a Reply to Professor JS T ewcomb, Mr. Hill, and others. 
By James Croll, LL.D., F.R.S* 
"VTINETEEN years ago the theory was advanced that the 
-L ^ Glacial Epoch was the result of a combination of phy- 
sical agents brought into operation by an increase in the 
eccentricity of the earth's orbit. Few or no objections have 
been urged against what may be called the astronomical part 
of the theory; but the portions relating to these physical 
agencies, which are by far the most important part, have from 
time to time met with considerable opposition. Considering 
the newness of the subject, and the complex nature of many 
of these combinations of physical agencies, it would not be 
surprising if some of the original deductions in regard to 
them proved erroneous; but after long and careful reconsi- 
deration of the whole matter, I have not found reason to 
abandon any of them or alter them to any material extent. 
The only class of objections urged against the theory which 
I have as yet considered at length are those relating to the 
cause of ocean-currents, and their influence on the distribu- 
tion of heat over the globe ; and I think it will be admitted 
that the views which I have advocated on these points are 
now being pretty generally accepted. 
* From advance sheets of the 'American Journal of Science ' for 
Octoher 1883. 
Phil. Mag. S. 5. Vol. 16. No. 100. Oct. 1883. T 
