# Clock

A clock is an instrument that measures the passage of time and indicates, perhaps visually, audibly, or electronically, the presently measured time in units of some type.

## Quotes

* ... Early clocks were inaccurate by as much as half an hour a day, and had to be reset frequently with the aid of a sundial; breakdowns were numerous. The energies of the early masters seem to have gone as much into ornamenting their clocks as into making them more precise, for the construction of human and animal automata, as well as astronomical indicators, was quite popular. Finally, in the seventeenth century, the Dutch scientist Christian Huygens created the pendulum-regulated clock that resulted in a vast improvement in precision. By then the clock was ingrained in the European way of thinking as the artificial model of the cyclical processes of nature, and it was ready to serve as the prototype for the mechanization of a variety of tasks that had previously been performed by hand.
** J. David Bolter, Turing's Man: Western Culture in the Computer Age. University of North Carolina. 1984. p. 26. ISBN 0807841080.
* The invention of the mechanical clock, and the significant perceptual shift that attended it, provides rich and underexamined context for reading Chaucer’s works. Among social scientists it has become “textbook wisdom” that the late medieval invention of the mechanical clock transformed ideas about time.
** Nancy Mason Bradbury and Carolyn P. Collette, (2009). "Changing Times: The Mechanical Clock in Late Medieval Literature". The Chaucer Review 43: 351–375. DOI:10.1353/cr.0.0027.
* By a clock we understand anything characterized by a phenomenon passing periodically through identical phases so that we must assume, by the principle of sufficient reason, that all that happens in a given period is identical with all that happens in an arbitrary period.
** Albert Einstein, "Principe de relativité" Archives des sciences physiques et naturelles (1910) ser. 4. 29 5-28 pp. 125–244, as quoted by Julian Barbour, "The Nature of Time" (Mar 20, 2009) p. 7, arXiv:0903.3489.
* … We are accustomed to regard as real those sense perceptions which are common to different individuals, and which therefore are, in a measure, impersonal. The natural sciences, and in particular, the most fundamental of them, physics, deals with such sense perceptions. The conception of physical bodies, in particular of rigid bodies, is a relatively constant complex of such sense perceptions. A clock is also a body, or a system, in the same sense, with the additional property that the series of events which it counts is formed of elements all of which can be regarded as equal.
** Albert Einstein, The Meaning of Relativity. Springer. 2013. p. 2. (1st edition, 1922)
* The 1967 General Conference on Weights and Measures defined the SI unit of time, the second, based on an atomic transition—specifically, between two hyperfine levels of the ground state of cesium-133. (See Physics Today, August 1968, page 60.) Although Cs atomic clocks remain the standard, their time might be running out. Their underlying atomic transition is excited by radiation with a microwave frequency around 9 × 10$^9$ Hz, and after decades of advances, a Cs clock’s frequency can be measured with a fractional uncertainty Δν/ν$_0$ of about one part in 10$^{16}$. But clocks based on optical transitions operate at frequencies around 10$^{14}$ Hz, which gives them an advantage in the push for lower uncertainty. (See the article by James Bergquist, Steven Jefferts, and David Wineland, Physics Today, March 2001, page 37.) The current record, 9.4 × 10$^{−19}$, was set in 2019 by an aluminum ion–based optical atomic clock at NIST.
** Christine Middleton, (2020). "Transportable atomic clocks achieve laboratory precision". Physics Today 73 (6): 20–21.
* The simplest and perhaps earliest clepsydra consisted of an earthen vessel with a small hole in the bottom. This was filled with water up to a certain mark and the water was allowed to trickle out of the hole. It would empty itself in approximately the same intervals of time. It was perhaps used for limiting the length of public speeches and the like. In fact there are quite a few references in Greek and Roman writings which would indicate this to have been a fact.
** Willis Isbister Milham, Time & timekeepers: including the history, construction, care, and accuracy of clocks and watches. New York: Macmillan. 1923. p. 49.
* The clock, not the steam-engine, is the key-machine of the modern industrial age. For every phase of its development the clock is both the outstanding fact and the typical symbol of the machine: even today no other machine is so ubiquitous. ... In its relationship to determinable quantities of energy, to standardization, to automatic action, and finally to its own special product, accurate timing, the clock has been the foremost machine in modern technics: and at each period it has remained in the lead: it marks a perfection toward which other machines aspire.
** Lewis Mumford, Technics and Civilization. University of Chicago Press. 2010. pp. 14–15. ISBN 0226550273. (1st edition 1934)
* We do not know when men first began to use instruments which were at all similar to modern sundials. A stone fragment in a Berlin museum is thought to be the earliest known sundial, dating from about 1500 B.C. The Bible mentions what some authorities take to have been a sundial (although the meaning is by no means certain) in the days of Ahaz, king of Judah some 700 years before Christ ... About a century later the Greek philosopher and astronomer Anaximander of Miletus is said to have introduced the sundial into Greece.
** Albert Edmund Waugh, Sundials: Their Theory and Construction. New York: Dover Publications. 1973. p. 3. ISBN 0486229475.

## External links

* Encyclopedic article on Clock on Wikipedia
* The dictionary definition of clock on Wiktionary