古人的一天,从晚上十一点开始

The day, for most people, begins at daybreak or at zero o'clock. For the ancients it began at eleven at night. This note sets out why: the double-hour 子 (zi), the first of the twelve, is the moment of the day farthest from the sun, the hour of greatest yin — and it is exactly there that the day is held to turn, just as the winter solstice, the day of the year farthest from the sun, is the point at which the single yang returns. The twelve double-hours are then presented as a set of names drawn not from an abstract scale but from the ordinary round of the day; two of the twelve are mealtimes, which is itself evidence that the ancients ate twice a day. A double-hour is exactly two hours, and after the Tang each was divided into an initial (初, chu) and a medial (正, zheng) half, giving twenty-four divisions whose length matches the modern hour — the origin of the word xiaoshi, "small hour". The note traces the twelvefold division against the rival schemes of two, five and ten divisions, and dates its final form to the Taichu calendar reform of 104 BCE; it then gives the length of the ke (刻) under the hundred-ke and ninety-six-ke systems (14.4 minutes before 1670, 15 minutes after) and the five watches (更, geng) of the night. It closes by noting that the double-hour was measured by the sundial, and that clock time and solar time are not the same thing. The note is descriptive; it contains no predictive claims.

(This preprint has not been peer reviewed.)