he anomalies of the motion
of the Earth's axis: though I doubt not that other anomalies also will come
to light some ages hence. So difficult is it to observe motion so slow,
unless extending over a period of many centuries; on which account we still
fail to understand the intent of Nature, what she is driving after through
such inequality of motion. Let A be the pole of the Ecliptick, B C the
Ecliptick, D the Aequator; when the pole of the Earth near the arctick
circle of the Zodiack faces the point M, then there is an anomaly of the
praecession of the aequinox at F; {238} but when it faces N, there is an
anomaly of the praecession at E. But when it faces I directly, then the
maximum obliquity G is observed at the solstitial colure; but when it faces
L, there is the minimum obliquity H at the solstitial colure.

[Illustration]

_Copernicus' contorted circlet in the Arctick circle of the Zodiack._

Let F B G be the half of the Arctick circle described round the pole of the
Zodiack: A B C the solstitial colure: A the pole of the Zodiack; D E the
anomaly of longitude 140 minutes at either side on both ends: B C the
anomaly of obliquity 24 minutes: B the greater obliquity of 23 degrees 52
minutes: D the mean obliquity of 23 degrees 40 minutes: C the minimum
obliquity of 23 degrees 28 minutes.

{239} [Illustration]

[Illustration]

{240} The period of motion of the praecession of the aequinoxes is 25,816
Aegyptian years; the period of the obliquity of the Zodiack is 3434 years,
and a little more. The period of the anomaly of the praecession of the
aequinoxes is 1717 years, and a little more. If the whole time of the
motion AI were divided into eight equal parts: in the first eighth the pole
is borne somewhat swiftly from A to B; in the second eighth, more slowly
from B to C; in the third, with the same slowness from C to D; in the
fourth, more swiftly again from D to E; in the fifth, with the same
swiftness from E to F; again more slowly from F to G; and with the same
slowness from G to H; in the last eighth, somewhat swiftly again from H to
I. And this is the contorted circlet of Copernicus, fused with the mean
motion into the curved line which is the path of the true motion. And thus
the pole attains the period of the anomaly of the praecession of the
aequinoxes twice; and that of the declination or obliquity once only. It is
thus that by later astronomers, but especially by Copernicus (the Restorer
of Astronomy)[25