279 
history and chronology of their ancestors. These 
manuscripts, which contain a great number of 
dates, reckoning at the same time according to 
the Christian era, and according to the civil and 
ritual calendar of the natives, have been studied 
with advantage by the learned Carlos de Siguen- 
za, professor of mathematics at the university 
of Mexico ; by the Milanese traveller, Boturini 
Benaducei; by the Abbe Clavigero; and latterly 
by Mr. Gama, whose astronomical labours I 
have had occasion to mention in another work 
Finally, in 1790, a stone of enormous bulk, 
covered with characters evidently relative to the 
Mexican calendar, the religious festivals, and 
the days in which the Sun passes the zenith of 
the city of Mexico, was discovered in the founda- 
tions of the ancient teocalli. This seryed at the 
same time to clear up some doubtful points, and 
call the attention of some enlightened natives to 
the Mexican calendar. 
I endeavoured, not only during my stay in 
America, but after my return to Europe, to study 
carefully every thing that has been published 
on the division of time, and the mode of inter- 
calation among the Aztecks. I examined on 
the spot the celebrated stone found in the Plaza 
Mayor, and represented in the twenty-third 
^ Essai polit. sur le Mexiqiie, vol, 2, p. 24, dc I’erjition 
in 8 VO. 
