SCIENTIFIC SUMMARY. 
201 
surface relatively to the plane of the ecliptic and consequently to the great 
source of light and heat, the sun. The Rev. J. F. Twisden has lately communi- 
cated to the Geological Society a valuable paper connected with this subject, 
its purpose being, as he describes it, the discussion of the possibility of a 
displacement of the earth’s axis of figure under the conditions indicated in 
a question (suggesting the possibility of a displacement of the axis of figure 
from the axis of rotation amounting to 15° or 20°) put to mathematicians in 
a passage of the Anniversary Address delivered to the Geological Society by 
its president, J. Evans, Esq., on February 18, 1876. Mr. Evans suggested 
that the occurrence of a great elevation at some part of the earth’s surface 
might affect the geographical position of its poles. The treatment of the 
question is kinematical ; the forces by which the elevations and depressions 
might be effected do not come under discussion. In determining numerically 
the amount of the deviation from the formulas investigated, approximate 
numbers seem to be sufficiently exact for every useful purpose. The con- 
clusions arrived at are as follows : — 
1. The displacement of the earth’s axis of figure from the axis of rotation 
that would be effected by the elevations and depressions suggested in the 
question above referred to would be less than of angle. 
2. A displacement of as much as 20° could be effected by elevations 
and depressions of the kind suggested only if their heights and depths ex- 
ceeded by many times the height of the highest mountains. 
3. Under no circumstances could a displacement of 20° be effected by a 
transfer of matter of less amount than about a sixth part of the whole 
equatorial bulge. 
4. Even if a transfer of this quantity of matter were to take place, it need 
not produce any effect, or only a small effect, on the position of the axis of 
figure, e.g. if it took place in a way resembling that suggested in the ques- 
tion, it would produce a displacement amounting to but a small part of 20°. 
5. If, however, we suppose a deviation of the axis of figure from the axis 
of rotation amounting to as much as 20° to have been by any means brought 
about, the effect would be to cause a sort of tidal motion in the ocean, the 
greatest height of which would tend to be about twice the depth of the 
ocean. The author suggests as probable that the effect of this tendency 
would be to cause the ocean to sweep over the continents in much the same 
way that a rising tide sweeps over a low bank on a level shore. 
6. The notion that a large deviation of the earth’s axis of figure from its 
axis of revolution may be effected by elevations and accompanying depres- 
sions is at first sight an inviting way of bringing polar lands into lower 
latitudes, and thereby accounting for the more genial climate that is 
believed to have once prevailed in such countries as Greenland. The inves- 
tigation by which the above results have been obtained seems to show that 
the desired explanation is not to be sought in the direction indicated by Mr. 
Evans’s question. Whether there is any other agency by which a gradual 
displacement of the pole geographically could be effected is a question of 
far wider scope than that discussed in the present paper, and one which the 
author does not profess to determine. 
The Rocky Mountains in Colorado. — Dr. A. O. Peale discusses ( u Silli- 
man’s Journal,” March, 1877) the geological phenomena of the Rocky Moun- 
NEW SERIES, YOL. I. NO. II. P 
