Yet, as soon as you drive away, it inevitably starts having that problem again. If they had send that clock back to the Americas from Europe, they would have seen exactly the same phenomena occur. The clock — which kept exquisitely accurate time in Europe — would have begun running at the wrong rate in the Americas once again.
The reason would have been totally obscure to anyone living in the time of Galileo, but it began to make sense once we started to understand how gravitation worked. In general, there are only two factors that determine the period of a pendulum: its length, where Here on Earth, the gravitational force is what drives the swinging of a pendulum. If you move a pendulum just a little bit away from its equilibrium position, the force of gravity is what pulls it back towards the equilibrium position.
But we wrongly assumed, before Newton came along, that gravity worked the same way everywhere on the surface of the Earth. But the way gravitation works is that it attracts you to the center of the Earth, even as the entire mass of the planet attracts you. Because the Earth spins on its axis, it bulges at its equator and gets compressed at the poles.
The diameter of the Earth at the equator is 12, km, while at the poles its only 12, km. This difference is largely due to Earth's axial rotation.
The gravitational field on Earth varies not only with latitude, but also with altitude and in other As a result, the gravitational acceleration varies by a few tenths of a percent across Earth's surface. Other major population centers in the Americas were even further south, closer to the equator, exacerbating that difference.
Elevation changes can also make a difference, with lowland locations near the poles having the highest accelerations on Earth of up to 9. However, the latitude problem is particularly important when it comes to timekeeping, and we can see this just by doing a simple calculation.
From their invention in until the s, pendulum clocks were the most accurate timekeeping The watch was at last a commodity accessible to the masses.
Because women had worn bracelet watches in the 19th century, wristwatches were long considered feminine accoutrements. During World War I, however, the pocket watch was modified so that it could be strapped to the wrist, where it could be viewed more readily on the battlefield.
With the help of a substantial marketing campaign, the masculine fashion for wristwatches caught on after the war. Self-winding mechanical wristwatches made their appearance during the s. Housed in a partial vacuum to minimize the effects of barometric pressure and equipped with a pendulum largely unaffected by temperature variations, Riefler's regulators attained an accuracy of a tenth of a second a day and were thus adopted by nearly every astronomical observatory.
Further progress came several decades later, when English railroad engineer William H. Shortt designed a so-called free pendulum clock that reputedly kept time to within about a second a year.
Shortt's system incorporated two pendulum clocks, one a master housed in an evacuated tank and the other a slave which contained the time dials. Every 30 seconds the slave clock gave an electromagnetic impulse to, and was in turn regulated by, the master clock pendulum, which was thus nearly free from mechanical disturbances.
Although Shortt clocks began to displace Rieflers as observatory regulators during the s, their superiority was short-lived. In Warren A. Marrison, an engineer at Bell Laboratories in New York, discovered an extremely uniform and reliable frequency source that was as revolutionary for timekeeping as the pendulum had been years earlier.
Developed originally for use in radio broadcasting, the quartz crystal vibrates at a highly regular rate when excited by an electric current [ see illustration in box on opposite page ]. The first quartz clocks installed at the Royal Observatory in varied by only two thousandths of a second a day. By the end of World War II, this accuracy had improved to the equivalent of a second every 30 years.
Quartz-crystal technology did not remain the premier frequency standard for long either, however. Subsequent experiments in both the U. Today the averaged times of cesium clocks in various parts of the world provide the standard frequency for Coordinated Universal Time, which has an accuracy of better than one nanosecond a day. Up to the midth century, the sidereal day, the period of the earth's rotation on its axis in relation to the stars, was used to determine standard time. This practice had been retained even though it had been suspected since the late 18th century that our planet's axial rotation was not entirely constant.
The rise of cesium clocks capable of measuring discrepancies in the earth's spin, however, meant that a change was necessary. A new definition of the second, based on the resonant frequency of the cesium atom, was adopted as the new standard unit of time in The precise measurement of time is of such fundamental importance to science that the search for even greater accuracy continues.
Current and coming generations of atomic clocks, such as the hydrogen maser a frequency oscillator , the cesium fountain and, in particular, the optical clock both frequency discriminators , are expected to deliver an accuracy more precisely, a stability of femtoseconds quadrillionths of a second over a day [see Ultimate Clocks, by W.
Wayt Gibbs, on page 56]. Although our ability to measure time will surely improve in the future, nothing will change the fact that it is the one thing of which we will never have enough. William J. Andrewes is a museum consultant and maker of precision sundials who has specialized in the history of time measurement for more than 30 years. He has worked at several scholarly institutions, including Harvard University. Andrewes is a museum consultant and maker of precision sundials www.
For his contributions to horology, he was awarded the Harrison Gold Medal in Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Reckoning Dates ACCORDING TO archaeological evidence, the Babylonians and Egyptians began to measure time at least 5, years ago, introducing calendars to organize and coordinate communal activities and public events, to schedule the shipment of goods and, in particular, to regulate cycles of planting and harvesting.
Recent Articles by William J. Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Well, throughout our history there were several phases of clock designs, which origins are not always clear and their original designers are lost to the history.
Sundials are the first time measuring devices known to man. Created originally in Babylon over 6 thousand years ago, and developed into more functional state in Ancient Egypt, sundials became extremely useful analogue clock device that remained in continual use for many thousands of years after, even managing to survive until today.
The true beginning of sundial popularity in Egypt started with the creation of first obelisks — tall and slim stone structure whose shadow enabled easy reading of time from the circular segmented horizontal disc that was placed on the ground around it.
Transitgoers consulted bus schedules with both European and Turkish times. A paradoxical enterprise with unintended consequences, time reform often caused more chronological chaos than it resolved. Many Europeans needed convincing, too. France adopted a nationwide mean time in but refused to adopt the Greenwich meridian; politicians preferred to calculate the hours in Paris rather than suffer the national indignity of setting French time with an English observatory.
Daylight saving time, another pet project for time reformers, struck many as a plot to steal extra hours from workers. Others thought it was an unforgivable attempt to play God. Still others worried about an encroaching state. Personally, I like to choose my own time for these operations.
An assistant professor of history at the University of Pennsylvania, Ogle frames time reform chiefly as a story about globalization. Built impressively on archival research conducted in eight countries and multiple languages, her book reveals that worldwide integration has always been uneven and contested. She reminds us that transnational networks and flows are never neutral and that globalization is an ideological process. There is, however, more than one astonishing tale to be coaxed from the overlooked history of clocks and calendars.
Time reform also offers a startling, deeply relevant explanation of how technological change happens. Telegraphs and steamships and railways generated the future they did only because they were harnessed to a particular political vision: a liberal world order under European auspices.
High-minded concepts like uniformity, efficiency, and progress were as ideological as they were scientific.
Taking Western superiority for granted, they reflected European convictions about human reason and the remaking of the world. Synchronization made it easier for European elites to project their influence and sell their goods.
But losses mounted among the poor and the powerless.
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