1874.] Climate of the Glacial Period. 443 
But granted that the great geometricians could not have 
erred very much in their calculations, we may still, with- 
out presumption, enquire whether there are not other ele- 
ments of disturbance besides those they investigated. 
They assumed in their examination of the problem that the 
thickening of matter around the equator was a constant ° 
quantity, whereas there are evidences of great upheaval 
and depression in remote ages that may have altered the 
conditions of the question. The gradual heaping up of ice 
around the poles in the glacial period must have in some 
measure diminished the difference between the polar and 
the equatorial diameters. Many physicists believe that 
even now an elevation of land around the poles and a de- 
pression of land in the tropics is taking place. 
The protuberance around the equator is not a regular one, 
but the equatorial circumference approaches in general 
outline to an ellipse, of which the greater diameter is two 
miles longer than the other. At the time the above- 
mentioned calculations were made the data did not exist for 
determining the irregularity. To the non-astronomical 
mind it appears evident that this great difference in the 
equatorial diameters is an element of great importance in 
the calculations, and as it was not considered we cannot 
admit that the problem has yet been decided. The great 
preponderance of land in one hemisphere, not arranged 
around the pole of the earth but in a mass whose centre is 
situated near the English Channel, must also be a disturbing 
element of no mean importance. 
Our knowledge of the other planets teaches us that there 
is no limit to the obliquity of their axes. In Jupiter the 
axis is nearly perpendicular to its orbit, so that there is no 
change in the length of its day. In Saturn the obliquity is 
29, in Mars 303°, and in Venus it reaches the extreme 
amount of 75°, so that its tropics overlap considerably its 
arctic circle, and there are no temperate zones. The 
original cause of the inclination of the axes of the planets 
has never been demonstrated, and until this be done it may 
be allowable to suppose that changes may occur through 
the same cause. 
Lieut.-Col. Drayson has approached this question in a 
different manner.* Leaving out altogether the consideration 
of the cause, he contends that a variation of the obliquity 
is taking place. He shows that according to the observa- 
tions of the last four hundred years the obliquity of the 
* The Last Glacial Epoch. Chapman and Hall. 
