ing to the
inclined tunnelling would be of use for exact work, and no such lines
could be drawn when once the level of the upper end of the entrance
passage had been passed by the builders.

A plan would be available, however (not yet noticed, so far as I know,
by any who have studied the astronomical relations of the great
pyramid), which would have enabled the builders perfectly to overcome
this difficulty.

Suppose the line of sight down the entrance passage were continued
upwards along an ascending passage, after reflection at a perfectly
horizontal surface--the surface of still water--then by the simplest of
all optical laws, that of the reflection of light, the descending and
ascending lines of sight on either side of the place of reflection,
would lie in the same vertical plane, that, namely, of the entrance
passage, or of the meridian. Moreover, the farther upwards an ascending
passage was carried, along which the reflected visual rays could pass,
the more perfect would be the adjustment of this meridional plane.

To apply this method, it would be necessary to temporarily plug up the
entrance passage where it passed into the solid rock, to make the
stone-work above it very perfect and close fitting, so that whenever
occasion arose for making one of the observations we are considering,
water might be poured into the entrance passage, and remain long enough
standing at the corner (so to speak) where this passage and the
suggested ascending passage could meet, for Alpha Draconis to be
observed down the ascending passage. Fig. 2 shows what is meant. Here D
C is the descending passage, C A the ascending passage, C the corner
where the water would be placed when Alpha Draconis was about to pass
below the pole. The observer would look down A C, and would see Alpha
Draconis by rays which had passed down D C, and had been reflected by
the water at C. Supposing the building to have been erected, as Lepsius
and other Egyptologists consider, at the rate of one layer in each year,
then only one observation of the kind described need be made per annum.
Indeed, fewer would serve, since three or four layers of stone might be
added without any fresh occasion arising to test the direction of the
passage C A.

[Illustration: Fig. 2.]

It is hardly necessary to remind those who have given any attention to
the subject of the pyramid that there is precisely such an ascending
passage as C A, and that as yet no explanation of the