Seismograph |
|
Modern seismographs have digital readouts but they operate still on the principles of inertia and relative motion. |
Seismograph |
|
Modern seismographs have digital readouts but they operate still on the principles of inertia and relative motion. |
A seismograph is an inertial pen
recorder that responds to waves propagated from distant earthquakes
or underground nuclear explosions. Seismographs record ground
acceleration. The base moves and the pen assembly (because of
inertia) does not.
The first known device for this
purpose was made in China around 2000 years ago. Brass balls
were supported in the mouths of dragons placed around a bowl.
The first ball to be disturbed indicated the direction - but
not the distance - of the epicenter. (Replica above left).