Richer observed pendulum clocks that lost time when moved from Paris to Cayenne, near the equator, indicating Earth flattening at the poles. Who was this observer?

Richer observed pendulum clocks that lost time when moved from Paris to Cayenne, near the equator, indicating Earth flattening at the poles. Who was this observer?

• A. Foucault
• B. Halley
• C. Gauss
• D. Richer

Answer: (D)

The main idea being tested is how local gravity varies with latitude and how that affects pendulum clocks. A pendulum’s period is T = 2π√(L/g). If gravity g is smaller, the period gets longer, so the clock runs more slowly. Paris sits at higher gravity than near the equator, so when pendulum clocks are moved from Paris to Cayenne, near the equator, they lose time because the weaker gravity there makes the pendulum swing a bit slower. This observation supports the idea that Earth is not the same everywhere in gravity; it’s flattened at the poles (an oblate shape) so gravity is slightly stronger at higher latitudes than near the equator. The observer who reported this specific Cayenne finding is Richer, who carried out the pendulum comparison as part of early geodetic work on Earth's shape. Other figures are known for different contributions—Foucault for demonstrating Earth's rotation with a pendulum, Halley for celestial navigation and gravity work, Gauss for advances in geodesy and gravimetry—but this particular equatorial pendulum observation linking gravity variation to Earth’s shape is associated with Richer.

The main idea being tested is how local gravity varies with latitude and how that affects pendulum clocks. A pendulum’s period is T = 2π√(L/g). If gravity g is smaller, the period gets longer, so the clock runs more slowly. Paris sits at higher gravity than near the equator, so when pendulum clocks are moved from Paris to Cayenne, near the equator, they lose time because the weaker gravity there makes the pendulum swing a bit slower. This observation supports the idea that Earth is not the same everywhere in gravity; it’s flattened at the poles (an oblate shape) so gravity is slightly stronger at higher latitudes than near the equator. The observer who reported this specific Cayenne finding is Richer, who carried out the pendulum comparison as part of early geodetic work on Earth's shape.

Other figures are known for different contributions—Foucault for demonstrating Earth's rotation with a pendulum, Halley for celestial navigation and gravity work, Gauss for advances in geodesy and gravimetry—but this particular equatorial pendulum observation linking gravity variation to Earth’s shape is associated with Richer.