History of timekeeping devices
In medieval Europe, purely mechanical clocks were developed after the invention of the bell-striking alarm, used to signal the correct time to ring monastic bells.
Error factors in early pendulum clocks included temperature variation, a problem tackled during the 18th century by the English clockmakers John Harrison and George Graham.
Following the Scilly naval disaster of 1707, after which governments offered a prize to anyone who could discover a way to determine longitude, Harrison built a succession of accurate timepieces, introducing the term chronometer.
3rd century BC) is credited by the Greeks with the invention of a hemispherical sundial hollowed out of stone; the path of the shadow was divided into 12 parts to mark the time.
[15] Greek sundials evolved to become highly sophisticated—Ptolemy's Analemma, written in the 2nd century AD, used an early form of trigonometry to derive the position of the Sun from data such as the hour of day and the geographical latitude.
[26] The oldest description of a clepsydra, or water clock, is from the tomb inscription of an early 18th Dynasty (c. 1500 BC) Egyptian court official named Amenemhet, who is identified as its inventor.
[35][36] The Athenian philosopher Plato is supposed to have invented an alarm clock that used lead balls cascading noisily onto a copper platter to wake his students.
[47] In 1235, a water-powered clock that "announced the appointed hours of prayer and the time both by day and by night" stood in the entrance hall of the Mustansiriya Madrasah in Baghdad.
The hourglass was one of the few reliable methods of measuring time at sea, and it has been speculated that it was used on board ships as far back as the 11th century, when it would have complemented the compass as an aid to navigation.
[72] From the 15th century onwards, hourglasses were used in a wide range of applications at sea, in churches, in industry, and in cooking; they were the first dependable, reusable, reasonably accurate, and easily constructed time-measurement devices.
[76][77] The first innovations to improve on the accuracy of the hourglass and the water clock occurred in the 10th century, when attempts were made to slow their rate of flow using friction or the force of gravity.
[79] A treatise written by Robertus Anglicus in 1271 shows that medieval craftsmen were attempting to design a purely mechanical clock (i.e. only driven by gravity) during this period.
[80] Such clocks were a synthesis of earlier ideas derived from European and Islamic science, such as gearing systems, weight drives, and striking mechanisms.
[89][90] Although the verge and foliot was an advancement on previous timekeepers, it was impossible to avoid fluctuations in the beat caused by changes in the applied forces—the earliest mechanical clocks were regularly reset using a sundial.
[100] The most famous example of a timekeeping device during the medieval period was a clock designed and built by the clockmaker Henry de Vick in c.1360,[88][101] which was said to have varied by up to two hours a day.
[109] The need for an escapement mechanism that steadily controlled the release of the stored energy, led to the development of two devices, the stackfreed (which although invented in the 15th century can be documented no earlier than c.1535) and the fusee, which first originated from medieval weapons such as the crossbow.
[109] Leonardo da Vinci, who produced the earliest known drawings of a pendulum in 1493–1494,[110] illustrated a fusee in c. 1500, a quarter of a century after the coiled spring first appeared.
[112] During the 16th century, timekeepers became more refined and sophisticated, so that by 1577 the Danish astronomer Tycho Brahe was able to obtain the first of four clocks that measured in seconds,[113] and in Nuremberg, the German clockmaker Peter Henlein was paid for making what is thought to have been the earliest example of a watch, made in 1524.
[120] The Italian polymath Galileo Galilei is thought to have first realized that the pendulum could be used as an accurate timekeeper after watching the motion of suspended lamps at Pisa Cathedral.
[112] The pendulum clock outperformed all other kinds of mechanical timekeepers to such an extent that these were usually refitted with a pendulum—a task that could be done without difficulty[127]—so that few verge escapement devices have survived in their original form.
[129] The swing was reduced to around 6° after the invention of the anchor mechanism enabled the use of longer, heavier pendulums with slower beats that had less variation, as they more closely resembled simple harmonic motion, required less power, and caused less friction and wear.
[134] In measuring an accurate one-second pendulum, for example, the Italian astronomer Father Giovanni Battista Riccioli persuaded nine fellow Jesuits "to count nearly 87,000 oscillations in a single day".
[148] After the Scilly naval disaster of 1707, in which four ships were wrecked as a result of navigational mistakes, the British government offered a prize of £20,000, equivalent to millions of pounds today, for anyone who could determine the longitude to within 50 kilometres (31 mi) at a latitude just north of the equator.
It was powered with dry piles, a high voltage battery with extremely long life but the disadvantage of its electrical properties varying according to the air temperature and humidity.
[162][163] In 1857, the French physicist Jules Lissajous showed how an electric current can be used to vibrate a tuning fork indefinitely, and was probably the first to use the invention as a method for accurately measuring frequency.
[168] An electrical oscillator was first used to sustain the motion of a tuning fork by the British physicist William Eccles in 1919;[169] his achievement removed much of the damping associated with mechanical devices and maximised the stability of the vibration's frequency.
[170][note 8] The following decades saw the development of quartz clocks as precision time measurement devices in laboratory settings—the bulky and delicate counting electronics, built with vacuum tubes, limited their practical use elsewhere.
[172] Their inherent physical and chemical stability and accuracy has resulted in the subsequent proliferation, and since the 1940s they have formed the basis for precision measurements of time and frequency worldwide.
[206] The SI defined the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two electron spin energy levels of the ground state of the 133Cs atom.
Confound him too, Who in this place set up a sundial, To cut and hack my days so wretchedly Into small portions—When I was a boy, My belly was my sun-dial: one more sure, Truer, and more exact than any of them.
