Curator Thierry Lalande talks about decimal time (10 hours per day, 100 minutes per hour, 100 seconds per minute) put into effect in the French Republic in 1793. He points out that as we now measure time in shorter durations, our measurement system changes bases: specifically from base 24 (vegisimal) for hours in a day, to base 60 (sexagesimal) for minutes and seconds, then to base 10 (decimal) to subdivide the second.
The collection of scientific instruments at the Musée des Arts et Métiers (Paris, France) includes a few decimal clocks and pocketwatches. When filming the kilogram and meter standards, I learned about decimal time from Dr. Lalande, who is a curator of scientific instruments at the Musée. His section includes some decimal clocks made in the 1790s. Some of the timepieces show 10 hours and their subdivisions only; others also include duodecimal time markings.
During the French Revolution, the desire to convert all measurement systems to base 10 included changing the way time was named, managed and measured.
Since the 1750s, prominent French mathematicians and other scholars had discussed the benefits of decimalized calculations, and in 1793, Jean-Charles de Borda officially proposed decimal divisions for days and hours: 10 hours of 100 minutes. Each minute had 100 seconds (about 14% shorter than traditional seconds).
The calendar would keep 365 days (or 366 in leap years) but the 12 months would be of uniform duration, all having 30 days. These months were given new names that celebrated the seasons and farming, for example, fructidor was the third of the summer group of months (who suffixes were -dor) and named after fruit. Months were divided into 3 décades of 10 days, and the tenth day, called décadi, replaced Sunday as a day of rest. The remaining five or six days became holidays, not commemorating saints or kings, but activities considered to further humankind and the nation, such as virtue, labor and the Revolution itself.
While decimal-based weights, measures, and currency were eventually adopted in France, decimal time and the French Republican calendar failed. In September 1805, Napolean Bonaparte declared that in 1806 France would resume using the Gregorian calendar. Several scholars point to his desire to reconcile with the Church, as the Revolutionaries had used the 10-day "week" to divert attention away from traditional Sunday activities. The Republican calendar lasted about 12 years, but mandatory use of decimal time lasted only 197 days, from September 22, 1794 to April 7, 1795.