In the 4th century BCE, Aristotle thought that the motion of an object depended on the very nature of that object. The pendulum posed a problem for him: why does the mass at the end of the string, released from a certain height, not go directly to its natural place, which is below, but then rise upward again?
Much later, in the 17th century, while watching a chandelier in Pisa Cathedral swing as he was thoroughly bored during Mass, Galileo discovered the isochronism of pendulum oscillations: the amplitude of the swing certainly decreases as time passes, but the mass always takes the same amount of time to complete a round trip. Galileo used this to formulate a law: a pendulum always keeps the same period, which does not depend on the amplitude (the angle the string makes with the vertical).
In fact, Galileo's law is valid only when the amplitude is “small.” At the time, discrepancies were observed at sea. To calculate a latitude, one need only measure the height of the Sun, whereas to calculate a longitude, one must compare the local time with a reference time. This raised the problem of carrying the departure time, of taking clocks on board that were stable enough to keep accurate time.
The oscillation becomes constant
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Also in the 17th century, in order to carry out his astronomical observations, the Dutchman Christian Huygens was seeking an instrument that measured the passage of time more accurately. In 1656, he invented the principle of the pendulum clock. At the beginning of 1659, Blaise Pascal answered (under a false name) questions that he himself had asked about the cycloid, which he called the roulette. The cycloid is the locus traced by a point on a circle of radius R as it rolls, without slipping, along a straight line (for example, the valve of a bicycle wheel).
