inclination of the entrance-passage is 26 deg. 27', as Professor Smyth made
it, the exact date for this would be 3390 B.C.; if 26 deg. 40', as others
made it before his measurements, the date would be about 3320 B.C.,
which would suit well with the date 3300 B.C., since a century either
way would only carry the star about a third of a degree towards or from
the pole.

Now, when we inquire whether in the year 3300 B.C. any bright star would
have been visible, at southing, through the ascending passage, we find
that a very bright star indeed, an orb otherwise remarkable as the
nearest of all the stars, the brilliant Alpha Centauri, shone as it
crossed the meridian right down that ascending tube. It is so bright
that, viewed through that tube, it must have been visible to the naked
eye, even when southing in full daylight.

But thirdly, we must consider how the builders of the pyramid would
arrange for the observation of the sun at noon on every clear day in the
year.

They would carry up the floor of the ascending passage in an unchanged
direction, as it already pointed south of the lowest place of the noon
sun at mid-winter. They would have to turn the tunnel into a lofty
gallery, to increase the vertical range of view on the meridian. It
seems reasonable to infer that they would prefer so to arrange matters
that the upper end of the gallery would be near the middle of the
platform which would form the top of the pyramidal structure from the
time when it was completed for observational purposes. The height of the
gallery would be so adjusted to its length, that the mid-winter's sun
would not shine further than the lower end of the gallery (that is, to
the upper end of the smaller ascending passage). In fact, as the moon
and planets would have to be observed when due south, through this
meridional gallery, and as they range further from the equator both
north and south than the sun does, it would be necessary that the
gallery should extend lower down than the sun's mid-winter noon rays
would shine.

As it would be a part of the observer's work to note exactly how far
down the gallery the shadow of its upper southern edge reached, as well
as the moment when the sun's light passed from the western to the
eastern wall of the gallery, and other details of the kind; besides, of
course, taking time-observations of the moment when the sun's edge
seemed to reach the edge of the gallery's southern opening; and as such
observ