Analyses of Books. 
[June, 
39 8 
Six Lectures on Physical Geography. By the Rev. S. Haughton, 
M.D., D.C.L., F.R.S., &c. Dublin : Hodges, Foster, and 
Figgis. London : Longmans, Green, and Co. 
The work before us is one which for many reasons deserves our 
most hearty welcome. It is an exposition of some of the latest 
results of modern science, and though popular, in the sense of 
being intelligible to the educated lay public, it is not the less 
accurate, comprehensive, and thoughtful. To many well-meaning 
but timorous souls the author’s attitude with reference to certain 
burning questions will prove not a little salutary. Dr. Haughton 
is no rash and shallow theorist, but a writer whose sound learning 
and sobriety of judgment are beyond dispute. He is, further, a 
believer in a personal God, and in the authority of the Scriptures 
as a moral and spiritual revelation. But he finds no difficulty, 
on this account, in accepting the dodtrine of Evolution, whether 
as regards the heavenly bodies or their organic inhabitants, and 
in admitting a minimum of two hundred million years for the 
past life-time of our planet. 
Among the many interesting subjects dealt with in this volume 
we will first glance at one which has often been discussed in the 
“Journal of Science,” — to wit, the Glacial epoch. Dr. Haugh- 
ton rejedts “ with contempt ” the theories which refer this dreadful 
visitation to a change in the position of the earth’s axis of rota- 
tion. He also rejedts all solutions based upon the secular cooling 
of the earth. It is of course obvious that such a gradual cooling 
down, if it might serve to explain the advent of the Glacial 
epoch, could not possibly account for the return of a better tem- 
perature. The changes in geological climate he refers to the 
gradual cooling of the sun, involving a corresponding refrigera- 
tion of the earth’s surface. Glaciation he thinks due to a tem- 
porarily diminished rate of heat-radiation from the sun. A 
natural consequence of such a change would be the precipitation 
of the aqueous vapour suspended in the atmosphere. Now as 
this same watery vapour is one of the main agencies which pre- 
vent the earth from radiating into space most of the heat which 
it receives from the sun, and which thus moderate the cold of the 
night and of the winter, it follows that such a precipitation would 
be “ followed by an increased radiation of non-luminous heat 
into space from the earth’s surface.” Now, though we have no 
positive proof of a transient decline in the sun’s heating power 
during the Glacial epoch, we still know that bodies like our sun 
do not decrease in radiance at one uniform rate. They have been 
observed to fade down, and again to blaze forth with increased 
splendour. In supposing that the sun has once, or more than 
once, been thus dimmed, we merely assume in him such changes 
as have occurred elsewhere in the universe. As a necessary 
