In Egypt and Mesopotamia where irrigated agriculture appears early date, calendars jr accuracy arose about 4,000 'G. or earlier. Similarly and for same reason they occur China and India about 2,000 B.C. Other countries learned from them In central Amerien n calendar wa developed possibly about $00 B. C. consisting of 18, "months" of 20 days with five supplementary day, Old calendars tend to a Junar {ype of 12 moon (356 day), which 860 days, whence comes the accept lever was revised to a solar type of
ed graduation of the circle into 260 degrees. Tt was gradually. dis. covered that 305 or 300 days was more accurate and so five intercalary or epagomenal days were added to the 260, Even the odd quarter of the day was known in Egypt say in 4,000°B. C. and used in the Dor Star cycle' of 1460 years. (The actual' length of the Year tropical" "ie 305 "days five hours 48 minutes and 46.15 seconds).
The Lunar Month In many cases it was attempted to make the lunar mon synodical month or lunation) and essential fraction of the year, inter-salary months being added to certain years so as to keep the seasons approximately correct. (The mean Ianation is actually 29 days 12 hours 44 minutes and 2.87 seconds). Thus the Chinese year which starts with the new moon hearst to the epoch midway between the winter solstice and the spring equinox has months of 29 or in 19 years. The Jewish year commences with the moon nearest to the vernal equinox (Passover is at the full moon of that month) and: adds intercalary moons when necessary at the end of the year. The Mohammedan calendar is the only purely Lunar one, having 354 days, so that the seasons mit rotate once in 34 years. The early Greek and Roman years were probably the same, but records are faulty and incon-
Text read from the printed page and cleaned; old type leaves the occasional error.