5. Astronomical Clocks
During the 11th century in the Song Dynasty, the Chinese astronomer, horologist and mechanical engineer Su Song created a water-driven astronomical clock for his clock tower of Kaifeng City. It incorporated an escapement mechanism as well as the earliest known endless power-transmitting chain drive, which drove the armillary sphere. Contemporary Muslim astronomers also constructed a variety of highly accurate astronomical clocks for use in their mosques and observatories, such as the water-powered astronomical clock by Al-Jazari in 1206, and the astrolabic clock by Ibn al-Shatir in the early 14th century. The most sophisticated timekeeping astrolabes were the geared astrolabe mechanisms designed by Abū Rayhān Bīrūnī in the 11th century and by Muhammad ibn Abi Bakr in the 13th century. These devices functioned as timekeeping devices and also as calenders.
4. Verge Escapement
The verge (or crown wheel ) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by advancing the gear train at regular intervals or ‘ticks’. Its origin is unknown. Verge escapements were used from the 14th century until about 1800 in clocks and pocketwatches. Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks. This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate. Oscillating timekeepers are at the heart of every clock today.
3. The Clockmakers
The first professional clockmakers came from the guilds of locksmiths and jewellers. Clockmaking developed from a specialized craft into a mass production industry over many years. Paris and Blois were the early centers of clockmaking in France. French clockmakers such as Julien Le Roy, clockmaker of Versailles, were leaders in case design and ornamental clocks. Le Roy belonged to the fifth generation of a family of clockmakers, and was described by his contemporaries as “the most skillful clockmaker in France, possibly in Europe”. He invented a special repeating mechanism which improved the precision of clocks and watches, a face that could be opened to view the inside clockwork, and made or supervised over 3,500 watches. The competition and scientific rivalry resulting from his discoveries further encouraged researchers to seek new methods of measuring time more accurately. In Germany, Nuremberg and Augsburg were the early clockmaking centers, and the Black Forest came to specialize in wooden cuckoo clocks. n 1904, Alberto Santos-Dumont, an early aviator, asked his friend, a French watchmaker called Louis Cartier, to design a watch that could be useful during his flights. The wristwatch had already been invented by Patek Philippe, in 1868, but only as a “lady’s bracelet watch”, intended as jewelry. As pocket watches were unsuitable, Louis Cartier created the Santos wristwatch, the first man’s wristwatch and the first designed for practical use.
2. Quartz Oscillators
A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits. Piezoelectricity was discovered by Jacques and Pierre Curie in 1880. Paul Langevin first investigated quartz resonators for use in sonar during World War I. The first crystal-controlled oscillator, using a crystal of Rochelle salt, was built in 1917 and patented in 1918 by Alexander M. Nicholson at Bell Telephone Laboratories, although his priority was disputed by Walter Guyton Cady. Cady built the first quartz crystal oscillator in 1921.
1. Atomic Clocks
Atomic clocks are the most accurate timekeeping devices known to date. Accurate to within a few seconds over many thousands of years, they are used to calibrate other clocks and timekeeping instruments. The first atomic clock, invented in 1949, is on display at the Smithsonian Institution. It was based on the absorption line in the ammonia molecule, but most are now based on the spin property of the cesium atom. The idea of using atomic transitions to measure time was first suggested in 1879. The practical method for doing this became magnetic resonance, developed in the 1930s. In 1945, Rabi first publicly suggested that atomic beam magnetic resonance might be used as the basis of a clock and finally it came in 1949.