Although the first seismic instruments accurate enough to be used in the scientific study of earthquakes were invented by three Englishmen-- James Alfred Ewing, Thomas Gray, and John Milne--the instruments were created while the three men were working at the Imperial College in Tokyo, Japan.

The seismic instruments that Ewing, Gray, and Milne invented were known as seismographs, a term still in use today. Seismographs use the principle of inertia to record the movement of the earth during an earthquake. Imagine a pendulum hanging by a string. When an earthquake occurs, the ground starts to shake. The pendulum, however, owing to its inertia, is at first motionless. By comparing the position of the pendulum with the position of the ground during an earthquake, it is possible to record the shaking of the ground.

Although modern seismographs use complex electronics to record the ground shaking as accurately as possible, they still rely on the same basic concepts as the Ewing-Gray-Milne instruments. The figure below shows a Bosch-Omori seismograph, one of the early successors to the original Ewing-Gray-Milne seismographs in Japan.