nels under the other pyramids. Its length underground amounts
to more than 350 feet, so that, viewed from the bottom, the mouth, about
four feet across from top to bottom on the square, would give a sky
range of rather less than one-third of a degree, or about one-fourth
more than the moon's apparent diameter. But, of course, there was
nothing to prevent the observers who used this tube from greatly
narrowing these limits by using diaphragms, one covering up all the
mouth of the tube, except a small opening near the centre, and another
correspondingly occupying the lower part of the tube from which the
observation was made.

It seems satisfactorily made out that the object of the slant tunnel,
which runs 350 feet through the rock on which the pyramid is built, was
to observe the Pole-star of the period at its lower culmination, to
obtain thence the true direction of the north point. The slow motion of
a star very near the pole would cause any error in time, as when this
observation was made, to be of very little importance, though we can
understand that even such observations as these would remind the
builders of the pyramid of the absolute necessity of good
time-measurements and time-observations in astronomical research.

Finding this point clearly made out, we can fairly use the observed
direction of the inclined passage to determine what was the position of
the Pole-star at the time when the foundations of the great pyramid were
laid, and even what that Pole-star may have been. On this point there
has never been much doubt, though considerable doubt exists as to the
exact epoch when the star occupied the position in question. According
to the observations made by Professor Smyth, the entrance passage has a
slope of about 26 deg. 27', which would have corresponded, when refraction
is taken into account, to the elevation of the star observed through the
passage, at an angle of about 26 deg. 29' above the horizon. The true
latitude of the pyramid being 29 deg. 58' 51", corresponding to an elevation
of the true pole of the heavens, by about 30 deg. 1/2' above the horizon, it
follows that if Professor Smyth obtained the true angle for the entrance
passage, the Pole-star must have been about 3 deg. 31-1/2' from the pole.
Smyth himself considers that we ought to infer the angle for the
entrance passage from that of other internal passages, presently to be
mentioned, which he thinks were manifestly intended to be at the sam