The history of timekeeping devices dates back to ancient civilizations observing astronomical bodies. Sundials and water clocks originated in ancient Egypt, while incense clocks were used in China. Mechanical clocks were developed in medieval Europe after the invention of the bell-striking alarm; Henry de Vick built a mechanical clock around 1360 that was the basis for improvements in timekeeping for the next 300 years. The mainspring, invented in the 15th century, allowed small clocks to be built. Leonardo da Vinci produced the earliest drawings of a pendulum. The pendulum clock, designed by Christiaan Huygens in 1656, was more accurate than other mechanical timekeepers. The electric clock, invented in 1840, controlled the most accurate pendulum clocks until the 1940s, when quartz timers became the basis for precise measurement of time and frequency. Atomic clocks are the most accurate timekeeping devices in practical use today and are used to calibrate timekeeping instruments. Read more: <https://en.wikipedia.org/wiki/History_of_timekeeping_devices> _______________________________ Today's selected anniversaries: 1773: The hymn "Amazing Grace" was probably first used in a prayer meeting in Olney, England, without the music familiar to modern listeners. <https://en.wikipedia.org/wiki/Amazing_Grace> 1892: The immigration station on Ellis Island in New York Harbor opened, and would process almost 12 million immigrants to the United States over the course of its existence. <https://en.wikipedia.org/wiki/Ellis_Island> 1928: Joseph Stalin's personal secretary, Boris Bazhanov, crossed the Iranian border and defected from the Soviet Union. <https://en.wikipedia.org/wiki/Boris_Bazhanov> 1998: Argentinian physicist Juan Maldacena published a landmark paper initiating the study of AdS/CFT correspondence, which links string theory and quantum gravity. <https://en.wikipedia.org/wiki/AdS/CFT_correspondence> _____________________________ Wiktionary's word of the day: qualtagh: (Isle of Man) The first person one encounters, either after leaving one's home or (sometimes) outside one's home, especially on New Year's Day; a first-foot. <https://en.wiktionary.org/wiki/qualtagh> ___________________________ Wikiquote quote of the day:   Love — caritas — is an extraordinary force which leads people to opt for courageous and generous engagement in the field of justice and peace. It is a force that has its origin in God, Eternal Love and Absolute Truth. Each person finds his good by adherence to God's plan for him, in order to realize it fully: in this plan, he finds his truth, and through adherence to this truth he becomes free … To defend the truth, to articulate it with humility and conviction, and to bear witness to it in life are therefore exacting and indispensable forms of charity.   --Pope Benedict XVI <https://en.wikiquote.org/wiki/Pope_Benedict_XVI>