Page:Popular Science Monthly Volume 80.djvu/462

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THE POPULAR SCIENCE MONTHLY
PSM V80 D462 Longitudinal sections of the grand gallery.png
Longitudinal Sections of the Grand Gallery.

it overhangs the bottom about one foot eight inches on three sides, 39.5 inches at its southern top. The stones on the sides are carefully set in tiers, the sides themselves being oriented to the compass points. Its exact dimensions which we shall find telltale are:

Inches
Inclined length of floor 1,815.6
Same produced to south walk 1,883.0
Height 339.0

It is now of course walled in by stone on every side, but in the day of its use it undoubtedly stood open at the top, the horizontal passage in which it now ends at the summit having been the beginning of the platform of the whole pyramid, at that height. No records tell us this; our information comes from the gallery itself. Now if we calculate the angle from the vertical which the end of the cornice makes with the upper end of the floor we shall find it 6° (6° 20'). Remember that the gallery faces due south, so far as the builders could place it, that the latitude was 30° (29° 58' 51") and that the obliquity of the ecliptic was then 24° (24° 4'). Now subtract the second angle from the first to get the altitude of the sun at the summer solstice, and we have 6°. Consequently at that season the shadow of the gallery roof would just strike the south end of the gallery floor. A curious astronomic coincidence, you say. But go a little further. Let us calculate the angle from this same coping down to the end of the central incline on the