Pendulum Article

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http://granitestudio.org/2008/03/01/the-historical-record-for-march-1-2008-zhang-hengs-seismometer/

The Oldest Pendulum

Zhang Heng, a Han Dynasty poet and court official, contributed greatly to Chinese society, and not only through his astronomic perfections of the Chinese calender or his famous Clepsydra Water clock. No, his finest invention is the oldest seismometer, which he called the 候风地动仪 (Houfeng Didongyi).

The years 96-125 were among the most seismically active in China's history, with records of over 23 major quakes and many more destructive tremors. Zhang Heng designed his seismometer to enable the court to detect the rough location of seismic tremors. Joseph Needham, a prominent historian on science in ancient China, described the the device as:

“...(C)onsist(ing) of a vessel of fine cast bronze, resembling a wine-jar, and having a diameter of eight chi (1 chi= 8 in.) . It had a domed cover, and the outer surface was ornamented with antique seal-characters and designs of mountains, tortoises, birds, and animals. Inside there was a pendulum capable of lateral displacement along tracks in the eight directions, and so arranged a closing and opening mechanism.

Outside the vessel there were eight dragon heads, each one holding a bronze ball in its mouth, while round the base there sat eight (corresponding) toads, with their mouths open, ready to receive any ball which the dragons might drop. The toothed machinery and ingenious constructions were all hidden inside the vessel, and the cover fitted down closely all round without any crevice. When an earthquake occurred the dragon mechanism of the vessel was caused to vibrate so that a ball was vomited out of a dragon-mouth and caught by the toad underneath. At the same instant a sharp sound was made which called the attention of the observers." - See more at: http://granitestudio.org/

On March 1, 138 C.E., an earthquake triggered Zhang Heng's seismometer indicating a tremor to the north east. Days later, word arrived of a quake hitting present day Gansu. With Zhang Heng's device's proven value, it became the duty of the court astronomers, of which he was a number, to monitor it's functions.

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http://fairytail.wikia.com/wiki/Horologium

Horologium

Galileo Galilei, an Italian physicist, mathematician, astronomer, and philosopher who played an instrumental part in the Scientific Revolution, was the first to study the properties of pendulums. He discovered isochronism, which states that the period of a pendulum is independent of the width of its swing, which is a crucial property of pendulums as timekeepers.

However, the actual construction of the pendulum clock, which Galilei designed, did not begin until shortly before his death, and, sadly, he never lived to see its completion. In 1656, Christian Hyugens built the first pendulum clock, thus reducing the variation between clock models from 15 minutes, to fifteen seconds. Because the pendulum was so accurate as a timepiece, that clocks outfitted with it were shipped all over the known world. However, a few discrepancies did arise; for example, the clocks in Paris were two and a half minutes faster than the clocks of the same make and model in Cheyenne. Sir Isaac Newton explained this as the result of Earth's oblique shape, claiming that gravity increased with latitude. Due to this revelation, pendulums were soon a common sight aboard ships as the world's first gravimeters, rendering an accurate account of the shape of the planet.

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wikipedia.org/wiki/Foucault_pendulum

Planetary Greatness

In 1666, an English scientist named Robert Hooke began study on a pendulum free to swing in two directions, later called a conical pendulum. Using this device, Hooke was able to monitor the orbital motions of the planets. Hooke used inertial and radial motion to explain the motion of the conical pendulum to his friend and colleague, Sir Isaac Newton, which played a fundamental role in Newton's law of universal gravitation.

This property was later used by French physicist Leon Foucault in a grand display of the Earth's rotation cycle. While the knowledge of Earth's rotation was itself old news, Foucault's experiment a twenty eight kilogram weight suspended by a sixty seven meter long wire from the roof the the Pantheon in Paris- was the first time it had been displayed in such a simple experiment. The Foucault pendulum took thirty two hours to perform a rotation of three hundred and sixty degrees, and continues to do so in more modern models of the experiment.

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Time Lords:

A Smooth Ride

The pendulum's reign reached its peak with the introduction of the gridiron pendulum, which was invented in 1726 by John Harrison. It consisted of alternating rods of two different metals; one with lower thermal expansion -steel-, and one with higher thermal expansion-brass or zinc. The rods were connected by a frame so that an increase in length of the zinc rods pushed the weight up, shortening the pendulum.

With an increase in temperature, the low expansion steel rods made the pendulum longer, while the high expansion zinc rods made it shorter. By making the rods the correct lengths, the greater expansion of the zinc cancelled out the expansion of the steel rods, which had a greater combined length, and the pendulum stayed the same length with temperature variation.

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Time Lords:

Fall of a Dynasty

The pendulum clock's accuracy rose sharply with new innovations as it entered the 20th century, including quartz rods which made the gridiron pendulum unnecessary and unsightly. The pendulum had become a common household item, no longer bearing the notoriety granted a brainchild of Galileo. The rise of the electric clock in the 1930s, despite having existed officially for ninety years by then, was, ultimately, it's downfall.

The pendulum was, of course, still a critical part of the mechanism, but it was no longer the main focus. No more would one have to wind the face of an old Grandfather clock with a painful little key, oh, no! just plug in this new apparatus that does it all for you. The hullabaloo raised over this new sensation which had, until recently, been inaccessible to the general public forced the pendulum clock into near obscurity.

Time Lords:

Epilogue

Decades after the pendulum clock's "fall from grace," a new force had brought it back as a recognizable face for the new generations. Collectors have scoured the globe for the missing hour hand of the clock owned by Hooke's great great great grand-niece, the obsessive buyers bringing a whole new outlook on the clock market today.

Many of these marketers are middle aged or older, having found there is nothing left to do once the nest is empty. So they wrack their brains for something to do when all of a sudden, it hits them. Why not scour the globe on the search for Grandma Betsy's Uncle's son's old cock that was in that one photograph that may or may not have included Hitler? I'm tired.

Photo credit: projectnerd.com

Time Lords:

A Rough Start

The pendulum's initial use as the world'd most accurate timepiece was unusurped until the invention of the quartz clock in the nineteen thirties. Despite this, the pendulum clock faced many difficulties throughout it's reign as "Time Lord."

One such obstacle was the slight changes in length the pendulum rod faced through exposure to variations in temperature. This phenomenon was first recorded when people began noticing that their clocks ran slower in the summer, often by as much as a minute per week. The thermal expansion of pendulum rods was first studied by Jean Picard in sixteen sixty nine, and he discovered that pendulums with steel rods will expand by 11.3 parts per million with every increase in degrees Celsius, which caused clocks equipped with them to lose 9 seconds per day with every increase in temperature. Wooden rods did not expand as much- only around 6 seconds-, and were used much more widely after this discovery.

The first successful response to this problem was the mercury pendulum, designed by George Graham. Mercury, as a liquid metal that expands in response to changes in temperature, was placed within the pendulum's weight. Thus, as the temperature rose and the rod became longer, the mercury would expand and bring the pendulum's center of mass closer to its pivot point, and in that way counteracting the change in clock speed with the changing of the seasons.