The Fruits of Civilization (3) Clocks

Clocks

Time management is an oxymoron. Time is beyond our control, and the clock keeps ticking regardless of how we lead our lives. Priority management is the answer to maximizing the time we have. ~ American author John Maxwell

There’s no sense talking about priorities. Priorities reveal themselves. We’re all transparent against the face of the clock. ~ American columnist Eric Zorn

Our endeavors bathe in the fluid river of time. The clock is one of the oldest inventions. Horology is the study of timekeeping.

In olden times, the technology applied to timekeeping depended upon the scale desired. The ancients placed stones on landscapes to capture the days of the year. Stonehenge is the most famous of these devices, but there were many throughout the ancient world. The earliest were built 10,000 years ago, perhaps even earlier. Stonehenge was built in 6 stages between 3100 and 1520 bce, beginning with the site as a burial ground.

The clepsydra, or water clock, was known to the ancient Babylonians, though when it was invented has been lost in time. The earliest-known specimens date to the 16th century bce.

The simplest clepsydras were vessels with a bunghole at the bottom to let water leak out at a controlled rate. Marks on the side of the vessel indicated temporal passage. They were typically used to keep time during the night.

Greek astronomer Eratosthenes invented the first armillary sphere in 255 bce. An armillary sphere is a mechanical spherical device comprising hoops or rings.

In the early 2nd century ce, Chinese polymath Zhang Heng built a celestial armillary sphere that rotated in a diurnal cycle. Its movement was regulated by a clepsydra attached to a water wheel. Zhang’s water-powered armillary sphere, with its complex gears, had a profound influence on later Chinese astronomy and mechanical engineering.

Clepsydras had many uses. The Romans timed the speeches of orators with them. In the 16th century, Italian physicist Galileo used a mercury clepsydra to time his experiments on falling bodies.

The general principles behind Zhang’s celestial sphere led to the discovery of the escapement mechanism for clockwork in 8th-century China. In the 8th century, Buddhist monk and mechanical engineer Yi teamed with Liang Lingzan to create a bronze astronomical instrument, powered by water, that served as a clock.

This was not the first liquid-driven escapement, which had been described by the Greek engineer Philo of Byzantium in the 3rd century bce. Its use was for a washstand. Philo remarked that “its construction is similar to that of clocks,” indicating that escapement mechanisms had already been integrated in ancient water clocks.

Sundials arose by 1500 bce as a means to tell the time of day. Such shadow clocks were employed by Egyptian and Babylonian astronomers. Sundials existed in ancient China too, though little is known of their history.

Shadow clocks were introduced to the ancient Greeks in the 6th century bce by Anaximander, an early proponent of science. Greeks sundials were initially derived from Babylonian counterparts.

Having established geometry, the Greeks advanced sundial technology. Astronomer and mathematician Theodosius of Bithynia is said to have invented a universal sundial in the mid-2nd century bce capable of employment anywhere on Earth.

Shadow clock technology passed to the Romans and the Arabs. Greek dials indicated unequal hours, as they varied by season. Muslim astronomer Ibn al-Shatir invented the polar-axis sundial in 1371, which indicated equal hours any day of the year. Some 70 years later the technology appeared in Europe. Trade of goods was always accompanied by information, the lasting prize of which was technological.

The Sun was not an altogether reliable partner for time keeping, as it was easily obscured by clouds and insisted on disappearing over the horizon at the end of the day. Waterpower could be, but it presented a problem: how to deliver continuous power for mechanical escapement devices. The answer was gravity.

An escapement is a mechanism for regulating mechanical movement. In reference to clocks, a verge is a vertical spindle. The verge escapement was the first mechanical escapement, used for several centuries to ring bells in an alarum (alarm device) before being adapted to clocks in late-13th-century Europe.

In the earliest tower clocks to appear, a verge escapement drove an oscillating foliot: a weighted balance wheel. As to accuracy, these clocks might have been off by around an hour a day.

The verge was the only escapement used in mechanical clocks for the next 2 centuries. Their accuracy improved somewhat as continuous tinkering led to better mechanics. Verge escapements continued to be used into the mid-19th century in clocks and pocket watches.

A great leap in timekeeping accuracy came in 1656, with a clock using a pendulum and balance spring. It was made by Dutch scientist Christiaan Huygens, who patented his device the following year.

Huygens had been inspired by Galileo, who discovered isochronism, the key property that makes pendulums useful timekeepers. Isochronism refers to the fact that the period of a pendulum swing is about the same for different-sized swings, thanks to the constancy of gravity.

The balance wheel in Huygens’ clock was an incremental improvement over the foliot. Such early balance wheels were crude timekeepers, as they lacked a balance spring.

The idea of the balance spring came from observing that springy hog bristle curbs, added to limit the rotation of a verge, increased its accuracy.

English scientist Robert Hooke first applied a metal spring to a balance wheel in 1658. Huygens and Jean de Hautefeuille contemporaneously shaped the balance spring to its present spiral form in 1674. Adding a spring to the balance wheel made it a harmonic oscillator: the basis of every modern clock.

A spring balance wheel vibrated at a natural resonant frequency, resisting changes in its vibratory rate from friction or other disturbances. This crucial innovation greatly improved the accuracy of watches, from potentially being several hours off a day to perhaps 10 minutes.

The major source of inaccuracy left came from temperature variations affecting pendulum rod length and balance-spring strength. Various approaches were made to ameliorate both problems.

English clockmaker George Graham put liquid mercury in the bob of the pendulum in 1721. Heat caused the rod to expand, but so too the mercury, raising its level in the container, and so keeping the center of pendulum gravity the same.

In 1726, English clockmaker and carpenter John Harrison created a gridiron pendulum that had a grid of different metals in the pendulum such that its length was unaffected by temperature.

In 1753, Harrison compensated for the balance-spring temperature problem by applying a bimetallic “compensation curb” on a spring for marine chronometers. This yielded an accuracy within a fraction of a second per day, but the complexity of the fix meant that it was a dead end.

A simpler solution was found by French clockmaker Pierre Le Roy in 1765: make the balance wheel change size to compensate for temperature. This was then incrementally improved upon by others.

Decent compensation was first accomplished by making the balance spring from a sandwich of metals – steel and brass – based on their relative thermal expansion rates. This was tinkered with for a century to further accurize clocks.

Then the bimetallic balance wheel was made obsolete in the early 20th century by an advance in metallurgy. In 1896, Swiss physicist Charles Édouard Guillaume invented a nickel-steel alloy with negligible thermal expansion. This solved both the pendulum and balance-spring problems.

Pendulum-based clocks can be quite accurate. They served as reference time pieces in laboratories well into the 20th century.

The electric clock was first patented in 1840 by Scottish engineer Alexander Bain. Development of electronics in the later 20th century led to clocks with no moving parts except the hands that tell time.

Known since ancient times, crystalline silica (SiO2) is commonly called quartz. It is one of the most complex and abundant of materials: found throughout the world, and in living organisms.

Silica is a major constituent of those sun-drenched sandy beaches so beloved by egg-laying sea turtles and tourists on holiday. Silica can also tell time.

Quartz is piezoelectric: singing at a certain frequency when an electric current flows through it. The resonance of a quartz crystal depends on its size, shape, and the crystal plane of its cut. For clockwork, quartz also bears the admirable quality of being insensitive to ambient temperature.

Radio engineers in the early 20th century sought a precise, stable source of radio frequencies. They started with steel resonators. But then American physicist and electrical engineer Walter Guyton Cady discovered in 1921 that quartz resonated with less equipment and better temperature stability. Steel resonators disappeared within a few years.

Quartz clocks were soon appreciated as more accurate than their swinging sisters. Besides, pendulums dangling from the wrist cannot tell time.

Quartz wristwatches had to await the development of inexpensive semiconductor chips, which were not available until the late 1960s. Within 2 decades, quartz timepieces dominated both the clock and wristwatch markets.

Quartz clocks are quite accurate, but the final word in temporal acuity is the atomic clock, which employs some electromagnetic frequency as a standard, notably the spectrum of select atoms. An atomic clock catches the frequency signal of electrons emitted from atoms as they change energy levels.

The idea of using atomic transitions to measure time was first suggested in 1879 by Scottish mathematical physicist William Thomson, better known as Lord Kelvin. Polish-born American physicist Isidor Rabi developed magnetic resonance in the 1930s which made this practicable.

Computers now synchronize themselves through the Internet to time signatures provided by atomic clocks.

The hours of folly are measured by the clock, but of wisdom no clock can measure. ~ English poet William Blake

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Time is money. ~ American author Benjamin Franklin

Obsession with time begat the economic concept of efficiency. From this flowed a lasting imposition on labor: to consider workers as mechanistic inputs of production.

Time as a productive measure so infused many modern cultures as to have monochronic time – living by the clock – dominate peoples’ lives.

Time as money is unnatural and often stressful. It may be contrasted to socially oriented polychronic time, where people matter more than minutes.

Time has everything to do not only with how a culture develops, but also with how the people of that culture experience the world. ~ American anthropologist Edward Hall