In 132 AD, Zhang Heng a Chinese polymath, invented the worlds first seismometer, which could detect the direction of an earthquake from over 300 miles away. Heng called his invention Houfeng Didong Yi. Houfeng Didong Yi roughly translates into "instrument for measuring the seasonal winds and movements of the Earth". The Houfeng Didong Yi was a large bronze vessel, two meters in diameter, around the top there were eight dragons holding bronze balls in their mouths; when an earthquake occurred the dragons mouth would open and drop its' ball into a bronze toad at the base, and supposedly showing the direction of the earthquake. The first ever earthquake recorded by this seismograph was supposedly somewhere in the east. Days later, a rider from the east reported this earthquake.
James Forb, in 1844, constructed an inverted seismometer that consisted of a metal having a mass C moveable upon it. The rod was supported on a vertical cylindrical steel wire. The wire could be made more or less stiff by pinching it at a greater or lesser height by means of a screw S. By adjusting the stiffness of the wire, or the height of the ball, the free period of the pendulum might be altered. A pencil L placed on the prolongation of the metal rod wrote a record on a stationary, paper-lined, spherical dome I. The Screws E, acting on the support D, are used to help set the pendulum in an upright position.
In 1879 after spending less than three years in Japan , James Ewing designed Ewing's Common Pendulum seismograph. Shown in the cross-section are the ring-shaped bob A spanned by the cross bar C.
Attached to the middle of the cross-bar is a brass plate L which has a slot in it. The lever M rests loosely in the slot. Motion perpendicular to the slot and is not affected. Another lever, not shown, records the component of horizontal motion parallel to the slot. In this way the horizontal ground motion is resolved into two perpendicular components.
Attached to the middle of the cross-bar is a brass plate L which has a slot in it. The lever M rests loosely in the slot. Motion perpendicular to the slot and is not affected. Another lever, not shown, records the component of horizontal motion parallel to the slot. In this way the horizontal ground motion is resolved into two perpendicular components.
A year later, 1880, James Ewing improved his design by converting it to a horizontal-pendulum seismometer. A light frame F is pivoted at points A and B so as to swing like a garden gate around the axis of rotation AB. At the axis of percussion of the frame is pivoted the cylindrical mass of M; the mass was pivoted on a light frame in order to obtain maximum inertia for a given distance of the axis of percussion from the axis of rotation.
Modern seismometers use electronic sensors, amplifiers, and recording devices. Some seismometers can measure motions with frequencies from 500 Hz to 0.001118 Hz.
Some modern instruments use a "triaxial" design, in which three identical motion sensors are set at the same angle to the vertical but 120 degrees apart on the horizontal. |
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MLA Citations: "When Was the First Recorded Earthquake?" When Was the First Recorded Earthquake? | Ask.com. Ask.com, n.d. Web. 23 Oct. 2014.
"The Early History of Seismometry (to 1900)." The Early History of Seismometry (to 1900). N.p., n.d. Web. 23 Oct. 2014.
Dewey, James, and Perry Byerly. "The Early History of Seismometry (to 1900)." The Early History of Seismometry (to 1900). N.p., n.d. Web. 23 Oct. 2014.
"Zhang Heng." Wikipedia. Wikimedia Foundation, 21 Oct. 2014. Web. 23 Oct. 2014.
"Seismometer." Wikipedia. Wikimedia Foundation, 20 Oct. 2014. Web. 22 Oct. 2014.
"The Early History of Seismometry (to 1900)." The Early History of Seismometry (to 1900). N.p., n.d. Web. 23 Oct. 2014.
Dewey, James, and Perry Byerly. "The Early History of Seismometry (to 1900)." The Early History of Seismometry (to 1900). N.p., n.d. Web. 23 Oct. 2014.
"Zhang Heng." Wikipedia. Wikimedia Foundation, 21 Oct. 2014. Web. 23 Oct. 2014.
"Seismometer." Wikipedia. Wikimedia Foundation, 20 Oct. 2014. Web. 22 Oct. 2014.