The details made out at present on the calendar are as follows:—the summer and winter solstices, the spring and autumn equinoxes, the two passages of the Sun over the zenith of Mexico, and some dates which possibly belong to religious festivals. The dates of the two zenith-transits are especially interesting; for, as they vary with the latitude, they must have been made out by actual observation in Mexico itself, and not borrowed from some more civilised people in the distant countries through which the Mexicans migrated. This fact alone is sufficient to prove a considerable practical knowledge of astronomy.
Besides this, the Mexican cycle of fifty-two years seems to be indicated in the circle outside the signs of days, and also the days in the priestly year of 260 days; but to make these numbers, we must allow for the compartments supposed to be hidden by the projecting rays of the sun.
The arrangement of the Mexican cycle of fifty-two years is very curious. They had four signs of years, tochtli, acatl, tecpatl , and calli ,— rabbit, canes, flint , and house ; and against these signs they ranged numbers, from 1 to 13, so that a cycle exactly corresponds to a pack of cards, the four signs being the four suits, thirteen