efined the beginning of exact astronomy, has been this, that several of
the circumstances insisted upon as determining that date imply a
considerable knowledge of astronomy. Thus astronomers must have made
great progress in their science before they could select as a day for
counting from, the epoch when the slow reeling motion of the earth (the
so-called precessional motion) brought the Pleiades centrally south, at
noon, at the time of the vernal equinox. The construction of the Great
Pyramid, again, in all its astronomical features, implies considerable
proficiency in astronomical observation. Thus the year 2170 B.C. may
very well be regarded as defining the introduction of a new system of
astronomy, but certainly not the beginning of astronomy itself. Of
course we may cut the knot of this difficulty, as Prof. Smyth and Abbe
Moigno do, by saying that astronomy began 2170 B.C., the first
astronomers being instructed supernaturally, so that the astronomical
Minerva came into full-grown being. But I apprehend that argument
against such a belief is as unnecessary as it would certainly be
useless.

And now let us consider how this theory accords with the result to which
we were led by the position of the great vacant space around the
southern pole. So far as the date is concerned, we have already seen
that the epoch 2170 B.C. accords excellently with the evidence of the
vacant space. But this evidence, as I mentioned at the outset,
establishes more than the date; it indicates the latitude of the place
where the most ancient of Ptolemy's forty-eight constellations were
first definitely adopted by astronomers. If we assume that at this place
the southernmost constellations were just fully seen when due south, we
find for the latitude about thirty-eight degrees north. (The student of
astronomy who may care to test my results may be reminded here that it
is not enough to show that every star of a constellation would when due
south be above the horizon of the place--what is wanted is, that the
whole constellation when towards the south should be visible at a single
view. However, the whole constellation may not have included all the
stars now belonging to it.) The station of the astronomers who founded
the new system can scarcely have been more than a degree or two north of
this latitude. On the other side, we may go a little further, for by so
doing we only raise the constellations somewhat higher above the
southern horizon, t