Christiaan Huygens

Christiaan Huygens (14 April 1629 - 8 June 1695), son of Constantijn Huygens, was an internationally renowned Dutch mathematician, physicist and astronomer.

Biography
Christiaan was born and raised in The Hague and studied law and mathematics in Leiden from 1645 to 1647 and in Breda from 1647 to 1649. Huygens went to Angers, France, to buy his PhD degree in law (1655), as was not unusual in those days. In 1663 he became a member of the British Royal Society. From 1666 to 1681 he lived in Paris as a member of the Académie des Sciences, founded by Colbert. In 1681 he moved back to The Hague.

Initially Huygens was mostly engaged in mathematics and was largely considered the leading figure among European mathematicians in the mid-seventeenth century. His work mainly concerned the then current problems of rectification, quadrature and cubature, determination of the center of gravity, determination of tangents of curves, and extrema. These were all problems that later were to be solved in differential and integral calculus by general methods, but before the inevention of calculus days they had to be tackled individually.

Later he dedicated himself to experimental and especially mathematical physics – primarily mechanics and optics. Huygens continued the development of classical mechanics, started by Galilei, by his research on falling and colliding bodies and pendulum and circular motion. By means of his theory of the physical pendulum he made a beginning with the dynamics of the solid body. He formulated and used the relativity principle of classical mechanics (the so-called Galilei relativity principle) and – by generalization of a statistical axiom of Torricelli – he arrived at the principle of conservation of mechanical energy in the homogeneous field of gravity.

The theory of the pendulum motion had a technical counterpart in the construction of a pendulum clock (1656), which considerably improved time keeping. This discovery instigated new theoretical investigations and technical improvements and variants, for example, a balance wheel with coiled spring in pocket watches. The aim was mainly to improve of time keeping at sea, thus enabling a better determination of the geographical longitude. In the field of optics Huygens was involved in the geometric theory of lenses and their application in telescopes and microscopes. He studied spherical aberration and invented the ocular (1662) named after him. He further developed a mechanistic theory of light, in which the propagation of light was considered as an extension of a collision in a subtle medium (ether). This collision theory is often described as an undulation or wave theory, but this should not be interpreted as a propagation of vibrations. Huygens’ light theory is based on a general principle, named after him. In the nineteenth century his collision theory of light was transformed into a vibration theory that dominated the entire nineteenth-century optics. By means of lenses, ground by himself and his brother Constantijn Jr., he constructed telescopes and microscopes, which he used for astronomical and microbiological observations. In 1655 he discovered the first of Saturn’s moons, Titan, and observed that this planet was surrounded by a ring. Huygens improved the air pump and used it for many experiments. He also tried to build an engine fueled by gunpowder, but never successfully completed one.