gard
to the southern pole of the heavens. The old constellations, the Altar,
the Centaur, and the ship Argo, extend within twenty degrees of the
pole, while the Southern Fish and the great sea-monster Cetus, which are
the southernmost constellations on the other side, do not reach within
some sixty degrees of the pole.

Of course, in saying that this peculiarity has not been considered, I am
not suggesting that it has not been noticed, or that its cause is in any
way doubtful or unknown. We know that the earth, besides whirling once a
day on its axis, and rushing on its mighty orbit around the sun
(spanning some 184,000,000 of miles) reels like a gigantic top, with a
motion so slow that 25,868 years are required for a single circuit of
the swaying axis around an imaginary line upright to the plane in which
the earth travels. And we know that in consequence of this reeling
motion the points of the heavens opposite the earth's poles necessarily
change. So that the southern pole, now eccentrically placed amid the
region where there were no constellations in old times, was once
differently situated. But the circumstance which seems to have been
overlooked is this, that by calculating backwards to the time when the
southern pole was in the centre of that vacant region, we have a much
better chance of finding the date (let us rather say the century) when
the older constellations were formed, than by any other process. We may
be sure not to be led very far astray; for we are not guided by one
constellation but by several, whereas all the other indications which
have been followed depend on the supposed ancient position of single
constellations. And then most of the other indications are such as might
very well have belonged to periods following long after the invention of
the constellations themselves. An astronomer might have ascertained, for
instance, that the sun in spring was in some particular part of the Ram
or of the Fishes, and later a poet like Aratus might describe that
relation (erroneously for his own epoch) as characteristic of one or
other constellation; but who is to assure us that the astronomer who
noted the relation correctly may not have made his observation many
hundreds of years after those constellations were invented? Whereas,
there was one period, and only one period, when the most southernmost of
the old constellations could have marked the limits of the region of sky
visible from some northern region.