1989 AD., Netherlands, Beatrix, Medallic Coinage, Constantijn and Christiaan Huygens commemorative, Monumunt B.V. mint, 10 Ecu, KM X 17.

Netherlands, Beatrix, Medallic Coinage, Ecu Series, Constantijn and Christiaan Huygens commemorative, Monumunt B.V. mint, Elst, issuer: Mauquoy - Tramaux & Co. B.v.b.a., Grobbendonk, 1989 AD.,
10 Ecu (38 mm / 19,37 g), copper-nickel-zinc, coin alignment ↑↓ (180°), plain edge,
Obv.: * CHR. HUYGENS * CONST. HUYGENS * / ADMOVERE OCULIS DISTANTIA SIDERA NOSTRIS , ("They brought the distant closer to our eyes") , jugate busts of Constantijn and Christiaan Huygens right; below, fish-symbol containing a W .
Rev.: DE NEDЄR - LANDEN / 10 / ECU / 19 - 89 , large "ECU", medieval sailing ship, 12 stars in ribbon border; just below sail, two circular mint symbols flanking, the right containing a horizontally mirrored M.
KM X 17 .

Christiaan Huygens, (14 April 1629 – 8 July 1695) was a prominent Dutch mathematician, astronomer, physicist and horologist, the second son of Constantijn Huygens, (1596–1687), who was a friend of mathematician and philosopher René Descartes and other famous persons of his era. His work included early telescopic studies elucidating the nature of the rings of Saturn and the discovery of its moon Titan, the invention of the pendulum clock and other investigations in timekeeping, and studies of both optics and the centrifugal force.
Huygens achieved note for his argument that light consists of waves, now known as the Huygens–Fresnel principle, which two centuries later became instrumental in the understanding of wave-particle duality. He generally receives credit for his discovery of the centrifugal force, the laws for collision of bodies, for his role in the development of modern calculus and his original observations on sound perception. Huygens is seen as the first theoretical physicist as he was the first to use formulae in physics.