Christiaan Huygens (April 14, 1629 - July 8, 1695) was a prominent Dutch mathematician, astronomer, physicist, probabilist, horologist and scientist. Huygens is remembered especially for his wave theory of light. He investigated the use of lenses in projectors and is credited as the inventor of the magic lantern. His work included early telescopic studies of the rings of Saturn and the discovery of its moon Titan. His invention of the pendulum clock was a breakthrough in timekeeping. He also developed a balance spring watch in the same period as Robert Hooke. Controversy over the priority persisted for centuries. He published major studies of mechanics and optics, and a pioneer work on games of chance. Shortly before his death, Huygens completed Cosmotheoros, published posthumously in 1698. In it he speculated on the existence of extraterrestrial life, on other planets, which he imagined was similar to that on Earth. He argued that extraterrestrial life is neither confirmed nor denied by the Bible, and questioned why God would create the other planets if they were not to serve a greater purpose than that of being admired from Earth. He died in 1695 at the age of 66.