johncarlosbaez

johncarlosbaez , 2 days ago to Random

Did you ever wonder why there are 90 degrees in a right angle instead of 100, and 24 hours a day instead of 10?

Perhaps you can blame Napoleon.

In 1795, as part of the French Revolution, the French passed a law requiring that clocks have 10 hours in a day, 100 minutes in an hour, and 100 seconds per minute. They also brought in a system of angles with 400 degrees in a full turn, or 100 degrees in a right angle. Now the earth would rotate 40 degrees in an hour - and thanks to how the meter was defined, each degree of latitude would be 100 kilometers long.

Of course, changing to the new system would require a lot of work. The economist Condorcet proposed that teams of unemployed wig makers be used to calculate mathematical tables with the new units. Why wig makers? Because after the revolution, aristocrats no longer needed them! (You don't need a wig if you don't have a head.)

The mathematical physicist Laplace was enthusiastic and had his watch converted to the new time. His great five-volume work Traité de Mécanique Céleste, was written using the new units of time and angle! But in general the metric system for time and angle did not catch on at all. And in 1806, Napoleon Bonaparte decreed that the French calendar should revert to the old style.

More details are here:

https://mathshistory.st-andrews.ac.uk/HistTopics/Decimal_time/
https://en.wikipedia.org/wiki/Decimal_time

Below, a picture of a French clock using decimal time made by Pierre Daniel Destigny, and now at the Fitzwilliam Museum in the Cambridge.