Editing Seismometer (section)

== History ==

The first seismometer was made in China during the 2nd century.<ref name="sivin" /> It was invented by [[Zhang Heng]], a Chinese mathematician and astronomer. The first Western description of the device comes from the French physicist and priest [[Jean de Hautefeuille]] in 1703.<ref name="Needham">{{cite book |author=Joseph Needham |title=Science and Civilisation in China: Paper and Printing |url=https://books.google.com/books?id=Lx-9mS6Aa4wC&pg=PA122 |access-date=16 April 2013 |year=1985 |publisher=Cambridge University Press |isbn=978-0-521-08690-5 |page=122 |quote=In the Southern Sung dynasty, gift money for bestowing upon officials by the imperial court was wrapped in paper envelopes (chih pao)}}</ref> The modern seismometer was developed in the 19th century.<ref name="Reitherman" />

Seismometers were placed on the Moon starting in 1969 as part of the [[Apollo Lunar Surface Experiments Package]]. In December 2018, a seismometer was deployed on the [[Mars|planet Mars]] by the ''[[InSight]]'' lander, the first time a seismometer was placed onto the surface of another planet.<ref name="NASA-20181219">{{cite news |last1=Cook |first1=Jia-Rui |last2=Good |first2=Andrew |title=NASA's InSight Places First Instrument on Mars |url=https://www.jpl.nasa.gov/news/news.php?feature=7310 |date=19 December 2018 |work=[[NASA]] |access-date=20 December 2018}}</ref>

=== Ancient era ===
[[File:EastHanSeismograph.JPG|thumb|Replica of [[Zhang Heng]]'s seismoscope ''Houfeng Didong Yi'']]
{{See also|List of Chinese inventions}}

In [[Ancient Egypt]], [[Amenhotep, son of Hapu]] invented a precursor of seismometer, a vertical wooden poles connected with wooden gutters on the central axis functioned to fill water into a vessel until full to detect earthquakes.

In [[AD 132]], [[Zhang Heng]] of China's [[Han dynasty]] is said to have invented the first seismoscope (by the definition above), which was called ''Houfeng Didong Yi'' (translated as, "instrument for measuring the seasonal winds and the movements of the Earth"). The description we have, from the [[Book of Later Han|History of the Later Han Dynasty]], says that it was a large bronze vessel, about 2 meters in diameter; at eight points around the top were dragon's heads holding bronze balls. When there was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and supposedly showing the direction of the earthquake. On at least one occasion, probably at the time of a large earthquake in [[Gansu]] in AD 143, the seismoscope indicated an earthquake even though one was not felt. The available text says that inside the vessel was a central column that could move along eight tracks; this is thought to refer to a pendulum, though it is not known exactly how this was linked to a mechanism that would open only one dragon's mouth. The first earthquake recorded by this seismoscope was supposedly "somewhere in the east". Days later, a rider from the east reported this earthquake.<ref name=sivin>{{cite journal |author=Sleeswyk AW, Sivin N |title=Dragons and toads: the Chinese seismoscope of BC. 132 |year=1983 |journal=[[Chinese Science]] |volume=6 |pages=1–19}}</ref><ref name=needham>{{cite book |last=Needham |first=Joseph |title=Science and Civilization in China, Volume 3: Mathematics and the Sciences of the Heavens and the Earth |place=Cambridge |publisher=Cambridge University Press |year=1959 |pages=626–635 |bibcode=1959scc3.book.....N}}</ref>

=== Early designs (1259–1839) ===
By the 13th century, seismographic devices existed in the [[Maragheh observatory]] (founded 1259) in Persia, though it is unclear whether these were constructed independently or based on the first seismoscope.<ref>{{Cite web |last=Szczepanski |first=Kallie |title=The invention of the Seismoscope {{!}} The Asian Age Online, Bangladesh |work=The Asian Age |access-date=2022-10-12 |url=http://dailyasianage.com/news/90282/?regenerate}}</ref> French physicist and priest [[Jean de Hautefeuille]] described a seismoscope in 1703,<ref name="Needham" /> which used a bowl filled with mercury which would spill into one of eight receivers equally spaced around the bowl, though there is no evidence that he actually constructed the device.<ref name=Oldroyd>{{Cite journal |doi=10.17704/eshi.26.2.h9v2708334745978 |volume=26 |last1=Oldroyd |first1=David |last2=Amador |first2=F. |last3=Kozák |first3=Jan |last4=Carneiro |first4=Ana |last5=Pinto |first5=Manuel |title=The Study of Earthquakes in the Hundred Years Following Lisbon Earthquake of 1755 |journal= Earth Sciences History|date=2007-01-01 |issue=2 |pages=321–370 |bibcode=2007ESHis..26..321O}}</ref> A mercury seismoscope was constructed in 1784 or 1785 by [[Atanasio Cavalli]],<ref>{{Cite journal |volume=13 |pages=1–21 |last=Ferrari |first=Graziano |title=Cultural and scientific value of seismology's heritage in Europe: why and how to preserve |journal=Cah. Cent. Europ. Geodyn. Seismol. |date=1997-01-01}}</ref> a copy of which can be found at the University Library in Bologna, and a further mercury seismoscope was constructed by [[Niccolò Cacciatore]] in 1818.<ref name=Oldroyd /> [[James Lind (naturalist)|James Lind]] also built a seismological tool of unknown design or efficacy (known as an earthquake machine) in the late 1790s.<ref>{{Cite book |last=Hart |first=Scott de |url=https://books.google.com/books?id=mIEOCwAAQBAJ&dq=earthquake+james+lind&pg=PA39 |title=Shelley Unbound: Discovering Frankenstein's True Creator |date=2013-07-22 |publisher=Feral House |isbn=978-1-936239-64-1 |pages=39 |language=en}}</ref>

Pendulum devices were developing at the same time. Neapolitan naturalist [[Nicola Cirillo]] set up a network of pendulum earthquake detectors following the 1731 Puglia Earthquake, where the amplitude was detected using a protractor to measure the swinging motion. Benedictine monk [[Andrea Bina]] further developed this concept in 1751, having the pendulum create trace marks in sand under the mechanism, providing both magnitude and direction of motion. Neapolitan clockmaker Domenico Salsano produced a similar pendulum which recorded using a paintbrush in 1783, labelling it a ''geo-sismometro'', possibly the first use of a similar word to ''seismometer''. Naturalist Nicolo Zupo devised an instrument to detect electrical disturbances and earthquakes at the same time (1784).<ref name=Oldroyd />

The first moderately successful device for detecting the time of an earthquake was devised by [[Ascanio Filomarino]] in 1796, who improved upon Salsano's pendulum instrument, using a pencil to mark, and using a hair attached to the mechanism to inhibit the motion of a clock's balance wheel. This meant that the clock would only start once an earthquake took place, allowing determination of the time of incidence.<ref name=Oldroyd />

After an earthquake taking place on October 4, 1834, [[Luigi Pagani]] observed that the mercury seismoscope held at [[Bologna University]] had completely spilled over, and did not provide useful information. He therefore devised a portable device that used [[lead shot]] to detect the direction of an earthquake, where the lead fell into four bins arranged in a circle, to determine the quadrant of earthquake incidence. He completed the instrument in 1841.<ref name=Oldroyd />

=== Early Modern designs (1839–1880) ===
In response to a series of earthquakes near [[Comrie, Perth and Kinross|Comrie]] in [[Scotland]] in 1839, a committee was formed in the [[United Kingdom of Great Britain and Ireland|United Kingdom]] in order to produce better detection devices for earthquakes. The outcome of this was an inverted pendulum seismometer constructed by [[James David Forbes]], first presented in a report by [[David Milne-Home]] in 1842, which recorded the measurements of seismic activity through the use of a pencil placed on paper above the pendulum. The designs provided did not prove effective, according to Milne's reports.<ref name=Oldroyd /> It was Milne who coined the word ''seismometer'' in 1841, to describe this instrument.<ref name="Ben-Menahem" /> In 1843, the first horizontal pendulum was used in a seismometer, reported by Milne (though it is unclear if he was the original inventor).<ref name=Mallet /> After these inventions, [[Robert Mallet]] published an 1848 paper where he suggested ideas for seismometer design, suggesting that such a device would need to register time, record amplitudes horizontally and vertically, and ascertain direction. His suggested design was funded, and construction was attempted, but his final design did not fulfill his expectations and suffered from the same problems as the Forbes design, being inaccurate and not self-recording.<ref name=Mallet>{{Cite journal |doi=10.1007/s10518-013-9444-5 |issn=1573-1456 |volume=11 |issue=3 |pages=715–861 |last=Musson |first=R. M. W. |title=A history of British seismology |journal=Bulletin of Earthquake Engineering |date=2013-06-01 |bibcode=2013BuEE...11..715M |s2cid=110740854 |doi-access=free}}</ref>

[[Karl Kreil]] constructed a seismometer in [[Prague]] between 1848 and 1850, which used a point-suspended rigid cylindrical pendulum covered in paper, drawn upon by a fixed pencil. The cylinder was rotated every 24 hours, providing an approximate time for a given quake.<ref name=Oldroyd />

[[Luigi Palmieri]], influenced by Mallet's 1848 paper,<ref name=Mallet /> invented a seismometer in 1856 that could record the time of an earthquake. This device used metallic pendulums which closed an [[electric circuit]] with vibration, which then powered an electromagnet to stop a clock. Palmieri seismometers were widely distributed and used for a long time.<ref>{{cite web |url=http://www.geophys.uni-stuttgart.de/oldwww/seismometry/seismo_htm/seismographen.htm |title=Seismographen |access-date=2011-02-18 |url-status=dead |archive-url=https://web.archive.org/web/20110318044124/http://www.geophys.uni-stuttgart.de/oldwww/seismometry/seismo_htm/seismographen.htm |archive-date=2011-03-18}}</ref>

By 1872, a committee in the United Kingdom led by [[James Bryce (geologist)|James Bryce]] expressed their dissatisfaction with the current available seismometers, still using the large 1842 Forbes device located in Comrie Parish Church, and requested a seismometer which was compact, easy to install and easy to read. In 1875 they settled on a large example of the Mallet device, consisting of an array of cylindrical [[bowling pins|pins]] of various sizes installed at right angles to each other on a sand bed, where larger earthquakes would knock down larger pins. This device was constructed in 'Earthquake House' near Comrie, which can be considered the world's first purpose-built seismological observatory.<ref name=Mallet /> As of 2013, no earthquake has been large enough to cause any of the cylinders to fall in either the original device or replicas.

=== The first seismographs (1880-) ===
The first seismographs were invented in the 1870s and 1880s. The first seismograph was produced by Filippo Cecchi in around 1875. A seismoscope would trigger the device to begin recording, and then a recording surface would produce a graphical illustration of the tremors automatically (a seismogram). However, the instrument was not sensitive enough, and the first seismogram produced by the instrument was in 1887, by which time [[John Milne]] had already demonstrated his design in [[Japan]].<ref name=Battlo>{{Cite book |publisher=Springer |isbn=978-3-642-36197-5 |pages=1–31 |editor1-first=Michael |editor1-last=Beer |editor2-first=Ioannis A. |editor2-last=Kougioumtzoglou |editor3-first=Edoardo |editor3-last=Patelli |editor4-first=Ivan |editor4-last=Siu-Kui Au |last=Batlló |first=Josep |title=Encyclopedia of Earthquake Engineering |chapter=Historical Seismometer |location=Berlin, Heidelberg |access-date=2022-10-17 |date=2021 |doi=10.1007/978-3-642-36197-5_171-1 |chapter-url=https://doi.org/10.1007/978-3-642-36197-5_171-1}}</ref>

[[File:Milne Horizontal Pendulum Seismograph.jpg|thumb|Milne horizontal pendulum seismometer. One of the [[Important Cultural Properties of Japan]]. Exhibit in the [[National Museum of Nature and Science]], [[Tokyo]], [[Japan]].]]

In 1880, the first horizontal pendulum seismometer was developed by the team of [[John Milne]], [[James Alfred Ewing]] and [[Thomas Lomar Gray|Thomas Gray]], who worked as [[Foreign government advisors in Meiji Japan|foreign-government advisors]] in Japan, from 1880 to 1895.<ref name="Reitherman">{{cite book |last=Reitherman |first=Robert |title=Earthquakes and Engineers: an International History |year=2012 |publisher=ASCE Press |location=Reston, VA |isbn=978-0-7844-1071-4 |pages=122–125 |url=http://www.asce.org/Product.aspx?id=2147487208&productid=154097877 |url-status=dead |archive-url=https://web.archive.org/web/20120726183407/http://www.asce.org/Product.aspx?id=2147487208&productid=154097877 |archive-date=2012-07-26}}</ref> Milne, Ewing and Gray, all having been hired by the [[Meiji Government]] in the previous five years to assist Japan's [[modernization]] efforts, founded the [[Seismological Society of Japan]] in response to an Earthquake that took place on February 22, 1880, at Yokohama (Yokohama earthquake). Two instruments were constructed by Ewing over the next year, one being a common-pendulum seismometer and the other being the first seismometer using a damped horizontal pendulum. The innovative recording system allowed for a continuous record, the first to do so. The first seismogram was recorded on 3 November 1880 on both of Ewing's instruments.<ref name=Battlo /> Modern seismometers would eventually descend from these designs. Milne has been referred to as the 'Father of modern seismology'<ref>{{Cite conference |last1=Herbert-Gustar |first1=A. L. |last2=Nott |first2=Patrick A. |title=John Milne : father of modern seismology |date=1980}}</ref> and his seismograph design has been called the first modern seismometer.<ref>{{Cite web |title=Who Invented the Seismograph? |access-date=2022-10-12 |url=http://www.theinventors.org/library/inventors/blseismograph.htm}}</ref>

This produced the first effective measurement of horizontal motion. Gray would produce the first reliable method for recording vertical motion, which produced the first effective 3-axis recordings.<ref name=Battlo />

An early special-purpose seismometer consisted of a large, stationary [[pendulum]], with a [[stylus]] on the bottom. As the [[earth]] started to move, the heavy mass of the pendulum had the [[inertia]] to stay still within the [[frame of reference|frame]]. The result is that the stylus scratched a pattern corresponding with the Earth's movement. This type of strong-motion seismometer recorded upon a [[smoked glass]] (glass with carbon [[soot]]). While not sensitive enough to detect distant earthquakes, this instrument could indicate the direction of the pressure waves and thus help find the epicenter of a local quake. Such instruments were useful in the analysis of the [[1906 San Francisco earthquake]]. Further analysis was performed in the 1980s, using these early recordings, enabling a more precise determination of the initial fault break location in [[Marin county]] and its subsequent progression, mostly to the south.

Later, professional suites of instruments for the worldwide standard seismographic network had one set of instruments tuned to oscillate at fifteen seconds, and the other at ninety seconds, each set measuring in three directions. Amateurs or observatories with limited means tuned their smaller, less sensitive instruments to ten seconds.
The basic damped horizontal pendulum seismometer swings like the gate of a fence.  A heavy weight is mounted on the point of a long (from 10&nbsp;cm to several meters) triangle, hinged at its vertical edge.  As the ground moves, the weight stays unmoving, swinging the "gate" on the hinge.

The advantage of a horizontal pendulum is that it achieves very low frequencies of oscillation in a compact instrument. The "gate" is slightly tilted, so the weight tends to slowly return to a central position. The pendulum is adjusted (before the damping is installed) to oscillate once per three seconds, or once per thirty seconds. The general-purpose instruments of small stations or amateurs usually oscillate once per ten seconds. A pan of oil is placed under the arm, and a small sheet of metal mounted on the underside of the arm drags in the oil to damp oscillations. The level of oil, position on the arm, and angle and size of sheet is adjusted until the damping is "critical", that is, almost having oscillation. The hinge is very low friction, often torsion wires, so the only friction is the internal friction of the wire.  Small seismographs with low proof masses are placed in a vacuum to reduce disturbances from air currents.

Zollner described torsionally suspended horizontal pendulums as early as 1869, but developed them for gravimetry rather than seismometry.

Early seismometers had an arrangement of levers on jeweled bearings, to scratch smoked glass or paper. Later, mirrors reflected a light beam to a direct-recording plate or roll of photographic paper. Briefly, some designs returned to mechanical movements to save money. In mid-twentieth-century systems, the light was reflected to a pair of differential electronic photosensors called a photomultiplier.  The voltage generated in the photomultiplier was used to drive galvanometers which had a small mirror mounted on the axis.  The moving reflected light beam would strike the surface of the turning drum, which was covered with photo-sensitive paper.  The expense of developing photo-sensitive paper caused many seismic observatories to switch to ink or thermal-sensitive paper.

After World War II, the seismometers developed by Milne, Ewing and Gray were adapted into the widely used [[Press-Ewing seismometer]].