Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources.
The word derives from the Greek σεισμός, seismós, a shaking or quake, from the verb σείω, seíō, to shake; and μέτρον, métron, measure and was coined by David Milne-Home in 1841, to describe an instrument designed by Scottish physicist James David Forbes.
Seismograph is another Greek term from seismós and γράφω, gráphō, to draw. It is often used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined than to modern systems, in which these functions are separated.
The first seismograph was invented in 132 A.D. by the Chinese astronomer and mathematician Chang Heng. He called it an "earthquake weathercock."
Around 132 AD, a Chinese scientist Chang Heng, invented the first seismoscope an instrument that could register the occurrence of an earthquake. Heng’s invention, ‘the dragon jar’ was a cylindrical jar with eight dragon heads arranged around its brim. Each dragonhead had a ball in its mouth. Around the foot of the jar were eight frogs, each directly beneath a dragonhead. During an earthquake, a ball dropped from a dragon’s mouth, and was caught by the frog.
Modern Seismograph
John Milne was the English seismologist and geologist who invented the first modern seismograph, and promoted the building of seismological stations. In 1880, three British scientists working in Japan, Sir James Ewing, Thomas Gray, and John Milne began to study earthquakes. They founded the Seismological Society of Japan. The society funded the invention of seismographs. Milne invented the horizontal pendulum seismograph in 1880.