The Measure of Time

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The Measure of Time


Beginning with the designs of Leonardo da Vinci (1452-1519) and Galileo Galilei (1564-1642), pendulums set in motion an evolution in accuracy and utility of clocks and watches. Various escapements managed motion into regular intervals. Balance wheels made miniaturization possible. Reliability became the holy grail of clockmakers, as temperature, torque, and friction were countered. Measurements became precise enough to justify adding a second hand, and clocks and watches became standard instruments for navigation and scientific experimentation. Ultimately, accurate clocks initiated changes beyond the measurement of hours, minutes, and seconds, creating mechanical devices, new philosophical concepts, and a new view of time itself.


There is only one measurement most people make every day—that of time. Clocks and watches are both widely used and highly personal devices. For timepieces—and a mechanical view of time—to permeate our culture, they had to become accurate and mobile. The first breakthrough came with a simple mechanism for dividing time into equal intervals—the pendulum. The person who had this insight was Galileo.

In Galileo's time, clocks were imprecise and used primarily for religious purposes. Mechanical clocks had existed since about a.d. 1000, powered by falling weights and controlled by verge escapements (bars with points at each end that rocked back and forth, allowing the energy of the falling weight to escape bit by bit by limiting the turning of a toothed gear). These clocks, at best, lost 15 minutes a day. The hours of the day were not yet standardized (a practice which came about with another invention, the train), and the modern sense of timekeeping, absolute, scientific, and independent of nature and tradition, did not yet exist.

But careful measurement had begun to come into its own during the Renaissance as observation and the scientific method took root. Nicolaus Copernicus (1473-1543) tracked the planets; Albrecht Dürer (1471-1528) used devices to add perspective to his drawings; explorers like Christopher Columbus (1451-1506) and Ferdinand Magellan (1480?-1521) took careful notes of winds, currents, and stars. Leonardo da Vinci, a keen observer with exceptional mechanical intuition, even sketched out a design of a pendulum clock. But, as was typical of Leonardo, the design remained hidden in his notebooks for generations.

Galileo was a major proponent of making science more quantitative, and taking advantage of the power of experimentation. When he first turned his attention to the pendulum in 1582, the device was the subject of the experiment, not the means for its measure. He used his own pulse to time the intervals of the swings of a chandelier and discovered that they were exceedingly regular, even when the angles were varied. He and his students observed oscillations of pendulums throughout an entire day to confirm that the swing of a pendulum has a constant period (now known not to be completely true). From this point on, Galileo used pendulums to measure short periods of times in his experiment, but he did not succeed in creating the first pendulum clock. Though weight power, gears, and escapements were familiar to him, Galileo was defeated in his attempts to build a pendulum clock by the difficulty in transferring the energy from the pendulum to a cog-wheel, and by problems with keeping the pendulum from slowing up and stopping.

The honor of building the first practical pendulum clock goes to the Dutch physicist and astronomer Christiaan Huygens (1629-1695). He completed his first model in 1656, using gravity not just to power the mechanism, but also to regularly give a "kick" to the pendulum to keep it going. By 1657 he had created a clock that was accurate to less than a minute per day, many times better than any clocks that preceded it. Huygens's triumph was not immediately celebrated in his day. In fact, there quickly were charges of plagiarism against the young, unknown scientist. It was only when Huygens revealed his detection of the ring of Saturn that he was accepted as an original who was extending, rather that stealing, the legacy of Galileo.

As valuable as the regulating quality of the pendulum was, it wasn't a very portable mechanism. In about 1500 Peter Henlein (1480-1542), a German blacksmith, created the first watch, powered by a spring. Henlein's use of a spring as a portable power could replace weights, but how could a pendulum be made equally portable? Here, Englishman Robert Hooke (1635-1703) is given credit for a clever leap of imagination. Hooke, an accomplished scientist who discovered refraction, first used the word "cell" as a biological term, and stated the inverse square law to explain the motion of planets, was fascinated by the physics of springs. He had discovered the principle (now known as Hooke's Law) that the stretching of a solid body is proportional to the force applied to it, and saw that a spring could be used to perform the task of a pendulum. His spiral balance spring (1660) was fixed to the movement at the outer end and to a friction-held collar at the other. The spring winds and unwinds, according to the balance of the mechanism, oscillating in exact analogy with the working of a pendulum. (As with the pendulum, the balance wheel must get a regular "kick," provided by the mainspring, to keep going.) By 1674, Huygens was making watches that included balance wheels and spring assemblies (with what was probably the first useful instance of the spiral balance spring) that were correct within 10 minutes over the period of a day.

About that same time, Englishman Thomas Tompion (1639-1714) also began making watches that used balance springs. He went on to become the most famous English clockmaker of his time, and introduced a number of improvements that made pendulum clocks more accurate and portable. Together with Edward Barlow and William Houghton, he also patented the cylinder escapement (1695). Here, the wheel's teeth alternately ride on the inside of the cylinder, then on the outside. This created a compact mechanism for regulating spring power, which allowed the making of flat watches. Jean de Hautefeuille (1647-1724), a French physicist interested in acoustics and tidal phenomena, claimed priority for the invention of the spiral balance spring, but is not generally credited with it (though he is credited with the invention of the virgule escapement for watches in 1670).

In the 1660s, William Clement invented an escapement that was so effective that it justified the use of a second hand. The anchor escapement (so-called because of its shape) rocks back and forth in the same plane as the toothed wheel, providing a highly controlled braking of the motion of the mechanism.


Over a 250-year period, timekeeping went from the village clocktower, accurate to the hour, to timepieces that were personal, portable, reliable, and accurate to the second. The very concept of time and its use changed during this period. Noon came not to mean when the Sun was at its zenith (apparent time), but the average of the times it was at its zenith (mean time), and humans began dividing their days by the rule of a mechanism rather than nature.

The ever more exact measurement of time was part of a general trend of measurement brought about by the successes of the scientific method. Numbers and standards were being applied to mass, volume, distance, heat, and other physical properties, inevitably moving toward the adoption of the metric system. Accurate measurement became essential to the progress of science and, on a more fundamental level, measurement allowed scientific concepts to be developed and expressed with equations, where pictorial and geometric methods had previously been dominant. The clock's contribution to science initially centered on astronomy, allowing an ever more detailed understanding of celestial dynamics. However, physics and engineering were not far behind.

The Age of Exploration was nearly over before the clock made a contribution. John Harrison's (1693-1776) chronometer allowed accurate determination of longitude, but Columbus, Magellan, and Vasco da Gama (1460?-1524) had depended on luck and "sailing the parallel" to avoid getting lost at sea. While this may have been adequate for adventurers, it was not sufficient for naval operations and was particularly unacceptable for commerce. Thus, the chronometer became a key tool in establishing sea power and facilitating worldwide trade.

Accurate clocks also made a commercial impact in factories by regulating work and synchronizing activity. This allowed more complex processes and greater efficiencies. In addition, the development of precision parts for clock-making made at least as large a contribution as accurate timekeeping did. As clocks came to represent shared, community time, rather that personal time, they especially needed regularity, consistency, and standardization. Accomplishing this required new tools and new skills. With this new capability, springs, gears, and other devices for managing energy found their way into other devices, including toys, automata, weapons, and industrial equipment. The success of these devices and the mechanical view they engendered led to a cultural change. Clockmakers began forming their own craft guilds as early as 1544, with the Guild of Clockmakers in Paris. These people shared a point of view. They actively sought to use their skills to solve other problems. It is no coincidence that inventors John Fitch (1743-1798), John Whitehurst, David Rittenhouse (1732-1796), Eli Terry (1772-1852), Alexander Bain (1818-1903), Benjamin Huntsman (1704-1776), and John Kay (1704-1780?), as well as French economist and politician Pierre du Pont de Nemours (1739-1817), were all clockmakers. The image of the clockmaker-inventor even entered literature (for example, Drosselmeyer in The Nutcracker) and became the precursor for nutty inventors and mad scientists that are prevalent in popular culture.

The clock exemplified a mechanical view that, with the rise of science, moved inexorably into the philosophical arena. With the development of Isaac Newton's (1642-1727) laws, the idea of a clockmaker god, who built the universe then stood aside to listen to it tick, took hold. By the 1700s this concept was an inspiration to Deists, Rationalists, and Materialists, and continues to be a lively subject of debate.

Western culture is obsessed with time (time is money), creating ever more accurate electronic digital clocks, as well as watches that are the hallmarks of fashion and beauty. Our machines also have an obsession with time. Every computer includes a clock, which is essential to its operation. And the watch, in particular, has been a model for interactive devices of the information age.

Accoding to historian Lewis Mumford: "The clock, not the steam engine, is the key machine of the modern industrial age. 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."


Further Reading

Asimov, Isaac. Isaac Asimov's Biographical Encyclopedia of Science & Technology. New York: Doubleday, 1976.

Barnett, Jo Ellen. Time's Pendulum: From Sundials to Atomic Clocks, the Fascinating History of Timekeeping and How Our Discoveries Changed the World. Chestnut Hill, MA: Harvest Books, 1999.

Landes, David S. Revolution in Time: Clocks and the Making of the Modern World, Cambridge, MA: Harvard University Press, 2000.

Yoder, Joella G. Unrolling Time: Christiaan Huygens and the Mathematization of Nature. Cambridge: Cambridge University Press, 1989.

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The Measure of Time

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