The first seismograph was invented by Zhang Heng, the court astronomer, at about 132 B.C. The seismograph was used to tell if there was an earthquake in China. With the slightest shake of an earthquake, a pendulum inside the jar would fall into a slot. A rod inside the slot would hit the ball causing it to fall and land in a toad's mouth with a big clang. Not only did it tell when the earthquake happened, but it told from which direction it came.

The first seismograph was 6 feet wide and 8 feet tall (just the jar), and was made out of bronze. Eight dragons and toads were placed at each direction, N. NE, E, SE, S. SW, W and NW. The ball would fall into the mouth of the toad facing the city that the earthquake occurred in. Although seismographs are very different today because we have more materials and better technology, they still do the same job, track earthquakes.

Today, seismographs vary in design and function. Generally, a heavy mass like a pendulum or large permanent magnet is the detecting instrument. A mechanical or optical recording devise is connected with the pendulum or the magnet. A mechanical system consists of a rotating drum having either a smoke covered surface marked by a stylus or a roll of paper marked by a pen or pencil. In an optical system, a beam of light is reflected by a mirror on a photographic paper or film. When tremors of the earth occur, the pendulum or the magnet remains still as the earth moves beneath.

Once, the ball dropped but no one felt an earthquake. People claimed that Zhang Heng's invention was fake. This went on for a few days until a messenger from one hundred miles to the northwest brought news of an earthquake. It had occurred the same time as when the ball dropped. The seismograph could detect earthquakes that were so far away that nobody could feel them!

I think that the seismograph was a very important invention. It can warn people of earthquakes and help prevent potential disasters and deaths. if it had not been invented, how would we be able to prepare ourselves for earthquakes today?

Bibliography:

A Message of Ancient Days.

Temple, Robert. The Genius of China. New York: Simon & Schuster, 1989