458 



THE POPULAR SCIENCE MONTHLY 



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 p.assage 

 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'). Eemember 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 coin- 

 cidence, 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 



