﻿The Aztec Calendar Stone. 



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plane of the meridian. By the means of this tubular passage they could 

 take observations upon the culminations of the sun and moon, by using 

 a mirror of mica or obsidian, to get the reflection of the rays to be visible 

 through the long narrow aperture. The passage at right angles was used 

 to obtain entrance or exit to the main chamber, and doubtless it served to 

 obtain observations on the sun at the vernal and autumnal equinoxes; and 

 there is seen also a tubular vertical passage of one foot in diameter, which 

 served to observe the two zenith transits of the sun. 



It is worthy of especial notice that the arched roof of the main cham- 

 ber is a groined arch, springing from the top of four walls of a square 

 chamber. The arching of the horizontal passages, of the vaulted roof of 

 chamber, and the wall of the vertical aperture for zenith observations, are 

 all of some kind of strong cement, one yard in thickness. The lower half 

 of the meridian passage and the walls of the chamber are made of dressed 

 stone — a true stone arch is seen over the doorway at the entrance of the 

 main chamber. The whole structure presents the appearance of a simple 

 mound of earth, 51 feet high and 126 feet in diameter. 



The horizontal passage being in the plane of the meridian, could not be 

 well used, except by the aid of reflecting mirrors ot mica or obsidian, 

 by which* means the movement of the sun to its maximum and minimum 

 declination could be followed, and the light transmitted through the long, 

 narrow, cylindrical aperture, and every meridian passage throughout the 

 year could be observed. Dupaix speaks of this as "either a temple or man- 

 sion of the dead, for it might have served both purposes." You will 

 also find a curious dome structure, with a vertical aperture, somewhat 

 resembling the structure just described in this same work of Lord 

 Kingsborough. (See Figure 34, Plate 16, Vol. IV., and description in 

 Vol. VI., p. 426.) 



While speaking of this singular building in which the true arch is seen 

 above the doorways, I would call attention to some ancient bridges de- 

 scribed by Dupaix. (See Lord Kingsborough, Vol. VI., p. 466.) In the 

 province of Tlalcala are two stone bridges, one near Los Reyes, built of 

 stone and cemented with mortar. " It has a sort of arch, which forms an 

 obtuse angle, springing from two side walls or buttresses." It is seven 

 feet high, seven feet broad, and has a width of forty-two feet. The 

 other bridge, which is not far away, is one hundred and two feet long, 

 thirty-six feet broad ; its perpendicular elevation is sixty feet. Both 

 bridges have four obelisks each, at their four angles, and are guarded 

 by parapet walls. This "sort of arch" consists of large stones, about 

 fourteen feet long, placed so that the ends abut against each other after 



