That Time When The French Divided The Day Into 10 hours

Jun 28, 2021 0 comments

For centuries we have used the sexagesimal system of measuring time, where each day is divided into 24 hours, each hour into 60 minutes and each minute into 60 second. Why do we do this? Is it out of habit, or is there any inherent advantage of measuring time by base 60?

The ancient Greeks were the first to introduce the concept of hour after Horae, the goddesses of the seasons and the natural portions of time. The number of Horae varied according to different sources, and while the most common is three, by Late Antiquity, their numbers had inflated to twelve, from which came the idea of dividing the day and the night into 12 hours each. The division of the hour into 60 minutes and of the minute into 60 seconds came from the Babylonians who used a sexagesimal system for mathematics and astronomy. The Babylonians divided the day into 360 parts, because that was their estimate for the number of days in a year. Diving a circle into 360 degrees was also their idea.

“Apollo with the Hours” by Georg Friedrich Kersting

“Apollo with the Hours” by Georg Friedrich Kersting (1822)

The Egyptians also used 12 hour days, possibly because there are twelve lunar cycles in a year, or probably they were easier to count on the 12 finger joints on each hand. In any case, these systems were adopted throughout the world and are now the standards of measuring time. But what if we change the standards?

Decimal Time

In 1754, French mathematician Jean le Rond d'Alembert proposed that all units of time should be divisible by ten:

It would be very desirable that all divisions, for example of the livre, the sou, the toise, the day, the hour, etc. would be from tens into tens. This division would result in much easier and more convenient calculations and would be very preferable to the arbitrary division of the livre into twenty sous, of the sou into twelve deniers, of the day into twenty-four hours, the hour into sixty minutes, etc.

In 1788, Claude Boniface Collignon, a French attorney, proposed dividing the day into 10 hours, each hour into 100 minutes, each minute into 1000 seconds, and each second into 1000 tierces. He also suggested a week of 10 days and dividing the year into 10 "solar months".

Jean-Charles de Borda modified the proposal, and based on this foundation the French Parliament decreed that “from midnight to midnight, is divided into ten parts, each part into ten others, and so forth until the smallest measurable portion of duration.”

Decimal time clock

Decimal time clock. Photo: Kcida10/Wikimedia Commons

The system officially went into force on November 24, 1793. Midnight began at zero hours (or 10 hours), and noon arrived at 5 hours. Each metric hour thus became 2.4 conventional hours long. Each metric minute became equivalent to 1.44 conventional minutes, and each metric second became 0.864 conventional second. Calculations became easier. Time could be written fractionally, for example, 6 hours 42 minutes became 6.42 hours and both meant that same thing.

To help people transition to the new time format, clock manufacturers began producing clocks with faces showing both decimal time and the old time. But the people never did transition to the new time. On the contrary, decimal time proved to be so unpopular that it was scrapped 17 months after it was introduced.

Decimal time was part of a larger attempt at decimalisation of everything by the French revolutionaries, which also included decimalisation of currency and metrication, and was introduced as part of the French Republican Calendar, which, in addition to decimally dividing the day, divided the month into three décades of 10 days each. Since this only accounted for 360 days, the five extra days required to approximate the solar year were placed at the end of each year without being count in any month. This calendar too was abolished at the end of 1805, and the entire plan was buried before it had time to fly.

Clocks from the French Revolution

Clocks from the French Revolution

After the decimal time fiasco, you would have expected that the French would never talk about it again, yet in the 1890s, Joseph Charles François de Rey-Pailhade, president of the Toulouse Geographical Society, once again proposed dividing the day, this time into 100 parts, called cés, each equal to 14.4 standard minutes, and each divided into 10 decicés, 100 centicés, etc. Worse still, the Toulouse Chamber of Commerce adopted a resolution supporting his proposal. Fortunately, sanity prevailed and the proposal received little backing outside the Chamber of Commerce.

Finally, a last ditch attempt was made in 1897 by the French scientific committee Bureau des Longitudes, with the mathematician Henri Poincaré as secretary. Poincaré adopted a compromise of retaining the 24-hour day, but dividing each hour into 100 decimal minutes, and each minute into 100 seconds. Again, the plan did not gain acceptance and decimal time was abandoned in 1900 for good. Nobody has dared to touch the clock again.

# Why are there 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day? Who decided on these time divisions?, The Guardian
# Why are there 24 hours in a day?, ABC Science
# Wikipedia


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