文档介绍：10250 - The Other Two Trees
You have a quadrilateral shaped land whose opposite fences are of equal length. You have fotrolled by a verge, an oscillating arm engaging with a gear wheel. It dates back to 1386.
Clocks driven by springs had appeared by the mid-15th century, making it possible to con- struct more compact mechanisms and preparing the way for the portable clock.
English spring-driven pendulum clocks were first commonly kept on a small wall bracket and later on a shelf. Many bracket clocks contained a drawer to hold the winding key. The earliest bracket clocks, made for a period after 1660, were of architectural design, with pillars at the sides and a pediment on top.
In 17th- and 18th-century France, the table clock became an object of monumental design, the best examples of which are minor works of sculpture.
The longcase clocks (also called grandfather clocks) are tall pendulum clock enclosed in a wooden case that stands upon the floor and is typically from 6 to feet ( to m) in height. Later, the name ``grandfather clock'' became popular after the popular song "My Grandfather's Clock," written in 1876 by Henry Clay Work.
One of the first atomic clocks was an ammonia-controlled clock. It was built in 1949 at the National Bureau of Standards, Washington, .; in this clock the frequency did not vary by more than one part in 108
Nuclear clocks are b