A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Who decided the day should be divided into 24 hours?

February 20, 1981

Dear Cecil:

My question arises from the fact that my kitchen happens to have both a boldly appointed digital clock and an old noisy analog thing my grandmother bought around 1940. I was delighted to discover quite by accident one bloodshot night that I could read the time on granny's clock from a far greater distance, and with much less light, than I could its digital counterpart. However, it occurred to me that were it to have been divided into eight equal sections, like a compass, reading it would be even less ambiguous. There is an obvious length to our day, but pray tell where is it written that it have 24 divisions called hours?

Dear P.:

Well, I could always find it in the back of the Growth in Arithmetic book, along with 16-1/2 feet to the rod. But maybe you had the abridged edition. In any case, we have the Babylonians to thank for our present system of timekeeping.

The number 12 held mystical significance for the ancients, owing to the fact that there were generally 12 full moons a year, and so they divided day and night into 12 parts each. The number 60, apart from being a multiple of 12, is evenly divisible by more integers than any lesser number, and thus was useful for dividing hours into minutes and seconds without the distraction of fractions.

The Babylonian calendar had 12 months of 30 days; since this left five days unaccounted for each year, every sixth year they repeated the month of Adar. The Romans, of course, introduced the present cockeyed system of 28-, 30-, and 31-day months.

While the Babylo-Roman method has a certain primitive charm, it does not make for ease of calculation, and there have been several attempts over the years to devise a more rational system. Perhaps the most famous of these was the social experiment conducted during the French Revolution.

In 1793, in an effort to sweep away the superstitious associations of the old method of timekeeping (you know how revolutionaries are), the French National Convention established a new calendar with 12 months of 30 days each, followed by five (six in leap years) "complementary days," which belonged to no month. Each month was divided into three 10-day "decades," and each day into two sections of 10 hours each. The hour was further divided into 100 "decimal minutes," which were in turn divided into 100 "decimal seconds."

The year began on the autumnal equinox, which happened to be the anniversary of the foundation of the Republic. Each month was given a descriptive name, e.g., Thermidor, July 19-August 17, "month of heat." Each day was also given its own name, some of which were less inspired than others, e.g., Eggplant, Manure, Shovel, Gypsum, Billy Goat, Spinach, and Tunny Fish. Even the French couldn't seriously have felt these represented a significant advance over old faves like Maundy Thursday. Also, on a more practical front, who wants to work a ten-day week?

Nontheless the French public made a valiant effort to implement the new system, going so far as to manufacture watches with concentric 10- and 12-hour dials. But ultimately the task proved to be beyond them. In 1806, after 13 baffling years of missed dentist appointments and overdue library books, they abandoned the revolutionary calendar. This was the only known defeat of Progress in the modern era prior to the establishment of the Illinois General Assembly. Gives you pause, when you think about it.

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