s purpose.

Astronomy teaches us to rely with certainty upon the permanence and
regular sequence of the seasons. The position of the Earth's axis as she
speeds along in her orbit through the unresisting ether remains
unchanged, and her rapid rotation has the effect of increasing its
stability. Yet, the Earth performs none of her motions with rigid
precision, and there is a very slow alteration of the position of her
axis occurring, which, if unchecked, would eventually produce a
coincidence of the equator and the ecliptic. Instead of a succession of
the seasons, there would then be perpetual spring upon the Earth, and,
although it would require a great epoch of time to bring about such a
change, there would result a condition of things entirely different to
what now exists on the globe. But, before the ecliptic can have
approached sufficiently near the equator to produce any appreciable
effect upon the climate of the Earth, its motion must cease, and after
remaining stationary for a time, it will begin to recede to its former
position. The seasons must therefore follow each other in regular
sequence, and throughout all time, reminding us of the promise of the
Creator, 'that while the Earth remaineth seed-time and harvest, and cold
and heat, and summer and winter shall not cease.'

CHAPTER VI

THE STARRY HEAVENS

The celestial vault, that, like a circling canopy of sapphire hue,
stretches overhead from horizon to horizon, resplendent by night with
myriad stars of different magnitudes and varied brilliancy, forming
clusterings and configurations of fantastic shape and beauty, arrests
the attention of the most casual observer. But to one who has studied
the heavens, and followed the efforts of human genius in unravelling the
mysteries associated with those bright orbs, the impression created on
his mind as he gazes upon them in the still hours of the night, when the
turmoil of life is hushed in repose, is one of wonder and longing to
know more of their being and the hidden causes which brought them forth.
Here, we have poetry written in letters of gold on the sable vestment of
night; music in the gliding motion of the spheres; and harmony in the
orbital sweep of sun, planet, and satellite.

Milton was not only familiar with 'the face of the sky,' as it is
popularly called, but also knew the structure of the celestial sphere,
and the great circles by which it is circumscribed. Two of those--the
colures--he all