Huygens returns to The Hague and continues his scientific work, focusing on mathematics, optics, and gravity. Despite facing health challenges, he remains intellectually active.

Huygens publishes 'Traité de la Lumière' (Treatise on Light), formally presenting his wave theory of light, a groundbreaking concept that would later become central to understanding light phenomena.

Huygens begins working on 'Cosmotheoros', a speculative work about extraterrestrial life and the possibility of inhabiting other planets. It showcases his imagination and philosophical musings.

Christiaan Huygens dies in The Hague, Netherlands, after a period of illness. He is buried in the Grote Kerk in The Hague. His unfinished work, 'Cosmotheoros', is published posthumously.