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France's failed experiment with decimal time
In 1793, revolutionary France attempted to overhaul timekeeping by dividing the day into 10 hours, each containing 100 minutes of 100 seconds. The radical shift was part of a broader effort to replace the Gregorian calendar with a 10-day week, aiming to rationalize and secularize societal structures.
Town halls across France installed decimal clocks, and official records adopted the new system. However, the transition proved chaotic, according to Finn Burridge, a science communicator at Royal Museums Greenwich in London. Converting existing clocks was cumbersome, and the rural population resisted the change, as the new 10-day week reduced rest days. The experiment collapsed within 17 months, though the revolutionary calendar lingered for nearly a decade.
The Sumerian origins of base-60
The roots of our modern timekeeping system trace back to the Sumerians, an ancient civilization in Mesopotamia (modern-day Iraq) that flourished between 5300 and 1940 BCE. Among their innovations-including irrigation and the plow-they developed the first known writing system, which incorporated a number system based on 60.
One theory suggests the Sumerians counted finger joints: each finger has three joints, and counting all 12 joints on one hand (excluding the thumb) while using the other hand to track sets of 12 could easily reach 60. This sexagesimal system became foundational for mathematics, astronomy, and eventually timekeeping.
"If you're developing numbers for practical purposes like accounting or dividing fields, having an easy way to perform calculations is invaluable," says Erica Meszaros, a historian of exact sciences at Brown University.
Martin Willis Monroe, a cuneiform expert at the University of New Brunswick, notes that the Sumerians used small clay tablets to record numbers, which evolved into cuneiform script. While the exact origin of the base-60 system remains unclear, its divisibility-by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60-made it highly practical for early societies.
From Egypt to Babylon: The birth of hours and minutes
The ancient Egyptians were the first to divide the day into hours, as seen in religious texts from around 2500 BCE. Early timekeeping devices, like diagonal star clocks on coffin lids (2100-1800 BCE), marked 12 nighttime hours. The choice of 12 may have stemmed from counting finger joints or aligning with a 10-day week and celestial observations, though the exact reason remains debated.
By 1500 BCE, sundials and water clocks appeared in Egypt, primarily for religious rituals rather than daily use. Rita Gautschy, an archaeoastronomer at the University of Basel, suggests many of these devices were likely votive gifts to deities. "We don't have much evidence of scientific timekeeping from that era," she says.
The Babylonians, who inherited the Sumerian sexagesimal system, further refined timekeeping. Around 1000 BCE, they divided the day and night into 12 seasonal hours each, with lengths varying by season. For astronomical calculations, they introduced smaller units: the ush (equivalent to four modern minutes) and the ninda (about four seconds), subdividing their double-hour beru by 60.
The Greek adoption and modern legacy
The Hellenistic era (post-330 BCE) saw a fusion of Egyptian and Babylonian ideas in Alexandria. The Greeks adopted the Babylonian astronomical time system, preserving its divisions to maintain continuity with existing data. "It worked well enough that later civilizations kept it," Meszaros explains.
While ancient societies used seasonal hours for daily life, smaller units like minutes and seconds only became practical with the advent of accurate timekeeping devices. Mechanical clocks in the 12th century were precise to within an hour, but it wasn't until the 18th century-with inventions like the H4 watch-that minutes and seconds entered common use.
Today, atomic clocks define the second based on caesium-133 atoms, ensuring precision for technologies like GPS and MRI machines. Yet the 60-second minute and 60-minute hour endure, a testament to the Sumerians' 5,000-year-old decision.
Why the system persists
France's brief experiment with decimal time underscores how deeply ingrained the sexagesimal system is. Despite its advantages, the metric time system failed to gain traction, while other revolutionary reforms-like the metric system for weights and measures-succeeded. As Burridge notes, "It was tried, but it didn't take off."
Claude-Antoine Prieur, a French revolutionary, argued in 1795 that decimal time offered no real benefits and risked undermining other metric reforms. The system's resilience lies in its utility: a human construct that, through centuries of use, has become indispensable.
