WORD OF THE DAY

A seismometer is a scientific instrument used to detect earthquakes. When the ground shakes, a seismometer can measure exactly how much it's moving up and down.

Seismometer comes from the Greek roots seismos, "a shaking," and metron, "a measure." During the 2nd century, a Chinese astronomer invented a basic version of the seismometer that scientists still use today. A simple seismometer is made from a frame that is very sensitive to motion and a weight suspended from it by a spring. The measurement of earthquake activity comes from comparing the relative motion of the weight compared with the frame.