Question: In what century did prominent Dutch mathematician, Christiaan Huygens, study Tractrix?
Context: Jan Jansz de Jonge Stampioen (1610, Rotterdam - 1653, The Hague) was a Dutch mathematician famous for his published work on spherical trigonometry.  In 1638 he moved to The Hague to become tutor of William II, Prince of Orange.  In 1644 he was employed to tutor Christiaan Huygens in mathematics. Treatise on Light (French: "Traité de la Lumière" ) is a 1690 book written by the Dutch polymath Christiaan Huygens on his wave theory of light.  Huygens' starting point was Descartes' theory, as presented in the "Dioptrique", which Huygens aimed to supplant.  Huygens' theory is also seen as the historical rival of Newton's theory, which was presented in the "Opticks". Huygens was an atmospheric entry probe that landed successfully on Saturn's moon Titan in 2005.  Built and operated by the European Space Agency (ESA), it was part of the "Cassini–Huygens" mission and became the first spacecraft ever to land on Titan and the furthest landing from Earth a spacecraft has ever made.  It was also the first landing on a moon other than our own.  The probe was named after the Dutch 17th-century astronomer Christiaan Huygens, who discovered Titan in 1655. A tractrix (from the Latin verb "trahere" "pull, drag"; plural: tractrices) is the curve along which an object moves, under the influence of friction, when pulled on a horizontal plane by a line segment attached to a tractor (pulling) point that moves at a right angle to the initial line between the object and the puller at an infinitesimal speed.  It is therefore a curve of pursuit.  It was first introduced by Claude Perrault in 1670, and later studied by Isaac Newton (1676) and Christiaan Huygens (1692). Christiaan Huygens, FRS ( or ; ] ) (Latin: "Hugenius" ) (14 April 1629 – 8 July 1695) was a prominent Dutch mathematician and scientist.  He is known particularly as an astronomer, physicist, probabilist and horologist. Huygens (also Huijgens, Huigens, Huijgen/Huygen, or Huigen) is a Dutch patronymic surname, meaning "son of Hugo".  Most references to "Huygens" are to the polymath Christiaan Huygens.  Notable people with the surname include: This article provides a Timeline of the Cassini–Huygens ( ) (commonly called Cassini) mission.  "Cassini" was a collaboration between the United States' NASA, the European Space Agency ("ESA"), and the Italian Space Agency ("ASI") to send a probe to study the planet Saturn and its system, including its rings and natural satellites.  The Flagship-class unmanned robotic spacecraft comprised both NASA's "Cassini" probe, and ESA's "Huygens" lander module which would be landed on Saturn's largest moon, Titan.  "Cassini" was the fourth space probe to visit Saturn and the first to enter its orbit.  The craft were named after astronomers Giovanni Cassini and Christiaan Huygens. An aerial telescope is a type of very long focal length refracting telescope, built in the second half of the 17th century, that did not use a tube.  Instead, the objective was mounted on a pole, tree, tower, building or other structure on a swivel ball-joint.  The observer stood on the ground and held the eyepiece, which was connected to the objective by a string or connecting rod.  By holding the string tight and maneuvering the eyepiece, the observer could aim the telescope at objects in the sky.  The idea for this type of telescope may have originated in the late 17th century with the Dutch mathematician, astronomer and physicist Christiaan Huygens and his brother Constantijn Huygens, Jr., though it is not clear if they actually invented it. Hendrik van Heuraet (1633, Haarlem - 1660? , Leiden) was a Dutch mathematician also known as Henrici van Heuraet.  He is noted as one of the founders of the integral, and author of "Epistola de Transmutatione Curvarum Linearum in Rectus" ["On the Transformation of Curves into Straight Lines"] (1659).  From 1653 he studied at Leiden University where he interacted with Frans van Schooten, Johannes Hudde, and Christiaan Huygens.  In 1658 he and Hudde left for Saumur in France.  He returned to Leiden the next year as a physician.  After this his trail is lost. The Cassini–Huygens mission ( ), commonly called Cassini, was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites.  The Flagship-class unmanned robotic spacecraft comprised both NASA's "Cassini" probe, and ESA's "Huygens" lander which would be landed on Saturn's largest moon, Titan.  "Cassini" was the fourth space probe to visit Saturn and the first to enter its orbit.  The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.
Answer: 1692