**Christiaan Huygens**

__Image:__ Painting by Caspar Netscher 1671

** Christiaan Huygens **

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* April 16, 1629 - † July 8, 1695 in The Hague

Mathematician, physicist and astronomer

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He is the founder of the wave theory of light without knowing the infinitesimal calculus, which was formulated in the same century by Isaac Newton and Gottfried Wilhelm Leibniz.

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He built the first pendulum clock based on the idea of Galileo Galilei. It was so accurate that the minute hand made sense. He published this in his work 'Horologium Oscillatorium' in 1673 and applied for a patent for both in 1675, which he released for general use. The script is one of the books "that changed the world".

**Period of a pendulum**

The restoring force of a pendulum results from the weight mg and the sine of the deflection angle (top sketch). Since the restoring force should sensibly increase evenly with the deflection of the pendulum, the smallest possible oscillations of a pendulum are important for accuracy.

The oscillation period T of the pendulum (see formula) results from its length l and the gravitational acceleration g. The mass of the pendulum does not affect the period of oscillation, but it does affect the energy required to sustain the oscillation, with larger masses being less prone to failure.

The formula applies to a full swing (back and forth), while watchmakers use a half swing for calculations: T = 2 seconds gives a length l of about 1 meter for a seconds pendulum.