When put in a suitable electronic circuit, this interaction between mechanical stress and electric field causes the crystal to vibrate and generate an electric signal of relatively constant frequency that can be used to operate an electronic clock display. If you apply an electric field to the crystal, it changes its shape, and if you squeeze it or bend it, it generates an electric field. Quartz clock operation is based on the piezoelectric property of quartz crystals. The performance of the Shortt clock was overtaken as quartz crystal oscillators and clocks, developed in the 1920s and onward, eventually improved timekeeping performance far beyond that achieved using pendulum and balance-wheel escapements. This allowed the master pendulum to remain free from mechanical tasks that would disturb its regularity. The slave pendulum gave the master pendulum the gentle pushes needed to maintain its motion, and also drove the clock's hands. This clock contained two pendulums, one a slave and the other a master. The Shortt clock almost immediately replaced Riefler's clock as a supreme timekeeper in many observatories. One of the most famous, the W.H. Shortt clock, was demonstrated in 1921. A true free-pendulum principle was introduced by R.J. Rudd about 1898, stimulating development of several free-pendulum clocks. Over the next century, refinements led in 1889 to Siegmund Riefler's clock with a nearly free pendulum, which attained an accuracy of a hundredth of a second a day and became the standard in many astronomical observatories. It kept time on board a rolling ship to about one-fifth of a second a day, nearly as well as a pendulum clock could do on land, and 10 times better than required to win the prize.
By 1761, he had built a marine chronometer with a spring and balance wheel escapement that won the British government's 1714 prize (worth more than $10,000,000 in today's currency) for a means of determining longitude to within one-half degree after a voyage to the West Indies. John Harrison, a carpenter and self-taught clock-maker, refined Graham's temperature compensation techniques and developed new methods for reducing friction. In 1721, George Graham improved the pendulum clock's accuracy to 1 second per day by compensating for changes in the pendulum's length due to temperature variations. And in London in 1671, William Clement began building clocks with the new "anchor" or "recoil" escapement, a substantial improvement over the verge because it interferes less with the motion of the pendulum. This improvement allowed portable 17th century watches to keep time to 10 minutes a day. His later refinements reduced his clock's error to less than 10 seconds a day.Īround 1675, Huygens developed the balance wheel and spring assembly, still found in some of today's wristwatches.
He even sketched out a design for a pendulum clock, but he never actually constructed one before his death in 1642.) Huygens' early pendulum clock had an error of less than 1 minute a day, the first time such accuracy had been achieved. (Galileo Galilei is credited with inventing the pendulum-clock concept, and he studied the motion of the pendulum as early as 1582. In 1656, Christiaan Huygens, a Dutch scientist, made the first pendulum clock, regulated by a mechanism with a "natural" period of oscillation.
These advances in design were precursors to truly accurate timekeeping. Although they ran slower as the mainspring unwound, they were popular among wealthy individuals due to their small size and the fact that they could be put on a shelf or table instead of hanging on the wall or being housed in tall cases. Replacing the heavy drive weights permitted smaller (and portable) clocks and watches. Like water flow, the rate was difficult to regulate.Īnother advance was the invention of spring-powered clocks between 15 by Peter Henlein of Nuremberg. Variations of the verge-and-foliot mechanism reigned for more than 300 years, but all had the same basic problem: the period of oscillation of the escapement depended heavily on the amount of driving force and the amount of friction in the drive. We have no evidence or record of the working models preceding these public clocks, which were weight-driven and regulated by a verge-and-foliot escapement. Then, in the first half of the 14th century, large mechanical clocks began to appear in the towers of several large Italian cities.
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