8. Final Years

For the rest of his life, Huygens remained in the Netherlands, an internationally famous scientist. He continued his research and publications to the end, living off the wealth of his family.

Initially he lived in his father’s house in The Hague, but after his father’s death, in 1687, he moved to the country house Hofwijk in nearby Voorburg, and there he spent his remaining years. After 1687 there was talk now and then of marriage, but Huygens never took that step.

During this period, Huygens occupied himself with further improvements of his pendulum clock, hoping to adapt it for maritime use, so that it could offer a solution to the problem of determining longitude at sea. The trials were, however, disappointing. He also turned his attention again to optics, and these studies led to a new theory of light, which he published in 1690 under the title Traité de la Lumière. With his theory, Huygens could explain the puzzle of the double refractive properties of Iceland spar (calcite).

In the meantime, a new generation of scientists had arisen, among which Isaac Newton and Gottfried Wilhelm Leibniz, with new ideas and methods. Huygens viewed their discoveries with great interest but also critically. In 1689, Huygens once again visited England, where, among others, he met Newton, whose magnum opus, the Philosophiae naturalis principia mathematica had appeared two years earlier. Huygens enjoyed the trip greatly. Unfortunately, he left no record of his discussions with Newton, with whom he had fundamental philosophical differences.

In 1695 Huygens’s health deteriorated rapidly. On 9 July of that year, after having drawn up a will, he passed away. He left his papers to the university of Leiden, where they remain to date. His instruments and telescope lenses remained in the possession of the Huygens family until 1754 when the collection was broken up at a public auction.