108 MEXICO AND CENTRAL AMERICA 



The true tropical year is determined by the revolution 

 of the earth around the sun and by the recurring 

 seasons. No agricultural people could neglect this time 

 period with its obvious relation to planting and harvest. 

 Reference has already been made to the notational 360 

 day year (tun) and to the conventional 365 day year 

 (haab). 



The haab was a vague year running ahead of the 

 true year by the accumulating amount of the days 

 which we intercalate on leap years: 1508 haab equaled 

 1507 tropical years. The Mayan months like those of 

 the ancient Egyptians slowly advanced through the 

 seasons. But the Mayas calculated an almost exact 

 correction for the excess of the true year over the 

 vague 365 day year. The excess amounts to about 

 .24 of a day and their correction seems to have been one 

 day in four years for ordinary purposes and 25 days in 

 104 years over longer stretches of time. This latter 

 correction is more accurate than was that of the Julian 

 calendar and nearly as accurate as that of the present 

 Gregorian calendar put into service as late as 1582. 



But if the "leap year" days were not interpolated, 

 of course, the named months had no fixed positions 

 in the year but swung slowly round the circle. Accord- 

 ing to the table of Landa, compiled about 1554, the 

 month Pop, which seems to have been regarded as 

 the first of the year in ancient as well as modern 

 times, began on July 16 O. S. Outside of the Mayan 

 area the retrogression of the months is attested by 

 actual statements of early Spanish writers. But the 

 conventional 365 day year was, after all, sufficiently 

 accurate to serve the needs of agriculturists and since 

 retrogression was only about one day in four years-, 

 associations between the months and the seasons would 

 hold true for the average lifetime. 



