Where this discovery comes from
The pendulum
Galileo noticed that a pendulum takes the same time for each swing whether it swings wide or narrow, as long as the swings are small — only its length changes the time. In 1656 Christiaan Huygens used that to build the first pendulum clock.
One thing to hold: A weight on a string, and a stopwatch.
Why it matters: Clocks went from losing about fifteen minutes a day to about fifteen seconds. In 1851 Léon Foucault hung a 28-kilogram bob in the Panthéon in Paris and showed the Earth turning beneath it.
What we don’t know: The story that Galileo first noticed it by watching a lamp swing in Pisa Cathedral was told later by his pupil Vincenzo Viviani; Galileo’s own notes and letters are the record, and the exact year is not certain.
Dates:
- 1656 Huygens builds the first pendulum clock.
- 1851 Foucault’s pendulum swings in the Panthéon.