56 
ANTHROPOLOGY: H. J. SPINDEN 
Proc. N. a. S. 
London Phil. Trans., A 183, 1892 (355); Meyer, Zur Kenntnis des negativen Druckes 
in Flussigkeiten, Halle, 1911. 
10 Lamb, Wilson, and Chaney, /. Ind. Eng. Chem., II, 1919 (420). 
11 Lemon, Physic. Rev., 14, 1919 (283). 
12 Chaney, Trans. Amer. Electrochem. Soc, 1919 (Advance sheets). 
13 Harkins, Brown, and Davies, /. Amer. Chem. Soc, 39, 1917 (354); Harkins, Davies, 
and Clark, Ibid., (541); Harkins and King, Ihid., 41, 1919 (970); these Proc^Bdings, 
5, 1919 (152). 
1* Harkins, these Proceedings, 5, 1919 (December). 
CENTRAL AMERICAN CALENDARS AND THE GREGORIAN 
DAY 
By Hhrbkrt J. Spind^n 
American Museum of Natural History, New York City 
Communicated by H, F. Osborn, December 23, 1919 
The day-for-day correlation of the Mayan, Aztecan, and Gregorian 
calendars depends upon mathematical relations and logical assumptions. 
First, as regards the archaic Mayan system of counting time, seen in 
inscriptions on monuments, the following assumptions are regarded as 
established : 
a. That the permutation cycle of 260 days made by combining 20 days 
and 13 numbers in sequence was continuously applied to days from a 
beginning day. 
h. That the notational system by which the index number of a day was 
written down was also continuously applied and that the designation of a 
day in the permutation and in the notation was constant and determinable. 
c. That the tun (360 days) and katun (7200 days) were not abstract 
time periods but instead were order values in the notational system and 
necessarily involved a context of the long count of days of the Mayas 
just as '06 or '19 necessarily involves a context in the long count of years 
that distinguishes European chronology. 
d. That the Mayan haab was a vague year of 365 days divided into 18 
long months of 20 days each and one short month of 5 days and that while 
the true length of the tropical year was known with tolerable accuracy to 
the Mayas no correction was directly applied to the haab count for fear 
of disorganizing the day count which was the common measure of all 
astronomical and mathematical cycles. 
As regards the records and time counts used by the Mayas of northern 
Yucatan at the time of the Spanish conquest it is regarded as proven: 
a. That an organic contact with the archaic long count was maintained 
through the orderly succession of tuns and katuns designated by the name 
of the day on which they were completed. 
h. That a true contact and correlation of the U Kahlay Katunob cycle 
of the historical summaries in the Books of Chilan Balam and the archaic 
