THE MAYAN CIVILIZATION 109 
fore an error amounting to one whole day has accumu- 
lated. In other words, the lunar calendar was brought 
into a fixed relation with the day count with an error of 
one day in 300 years. 
On the monuments a more or less orderly group of 
hieroglyphs following the Initial Series has been called 
the Supplementary Series. Several of these hiero- 
glyphs contain the symbol for the moon and the last 
one contains this symbol with the numerals 9 or 10 to 
the right or below. It has been suggested that this 
Fig. 44. The Last Glyph of the Supplementary Series: a, moon 
glyph; combined with the numeral 9 or 10 to indicate a 29 or a 30 
day lunar month. 
last glyph stands for a 29 or 30 day month, as the case 
may be, and that the Supplementary Series records 
the position of the Initial Series date in a lunar count. 
The Venus Calendar. The Mayan astronomers 
possessed a remarkable knowledge of the movements of 
the planets. In particular the apparent revolution of 
the planet Venus was used as the basis of what we may 
eall the Venus Calendar. ‘The mean synodical year of 
Venus (nearly 584 days) is divided in the Mayan books 
into four parts of 236 days (morning star), 90 days 
(superior conjunction), 250 days (evening star), and 
8 days (inferior conjunction). It is true that these 
divisions do not agree very closely with the actual divi- 
sions of the Venus year but we must remember that the 
observations were made without instruments, that the 
planet cannot be seen by the naked eye when close to 
