1875.] Variation in the Obliquity of the Ecliptie. 287 
obliquity at the date when the pole of the heavens was 
situated 180° in the circle from the date A.D. 2298. Such 
an extension of the obliquity would bring England within 
the arctic circle, and would supply those climatic conditions 
which geologists consider prevailed during the Glacial Epoch. 
Thus we have, first, the actual recorded observational facts 
proving a certain curve to have been traced during the past 
four or five centuries : secondly, geological evidence, indi- 
cating such a climatic change as would result from an 
extension of 12° or more in the obliquity. 
These two evidences are certainly strongly in favour of a 
possible increase in the obliquity, and, unless very powerful 
and convincing evidence can be brought in opposition 
thereto, must certainly tend to prove the fact. 
Let us, however, examine another problem. Let us 
grant that the plane of the ecliptic does slowly vary (of 
which variation, however, there is no proof from the 
recorded changes in star latitudes), the course of the earth 
round the sun would slightly vary; but it is possible that 
the earth’s axis would partake of this movement, and the 
pole of the heavens and pole of the ecliptic would then vary 
their relative distances just the same as if the plane of the 
ecliptic were at rest; and as it is a fact that the course of 
the pole of the heavens relative to the pole of the ecliptic 
is such a curve as that we have described it to be, we have 
actual facts on one side and theoretical conclusions on the 
other. 
Taking an abstra¢t view of the problem as far as it is 
here stated, we have the following as the two sides of the 
question relative to a possible variation of the obliquity :— 
On the one side we have a series of distances measured 
between the pole of the heavens and the pole of the 
ecliptic (termed the obliquity at various dates), and also the 
rate at which the pole of the heavens has decreased its 
distance from certain stars ; consequently the nature of the 
curve thus traced by the pole of the heavens can be ascer- 
tained without any great difficulty. This curve is not one 
imagined by a theorist, or supposed to be traced in conse- 
quence of certain assumptions connected with attraction 
and repulsion, but the curve is one that recorded facts prove 
to have occurred during at least 400 years, and this curve— 
if continued during 13,000 years—will produce a change in 
the obliquity or angular distance of the two poles, viz., that 
of the heavens and of the ecliptic of 353°, and would conse- 
quently bring portions of Great Britain within the arctic 
circle. 
VOL. V. (N.S.) 20 
