seismograph
- n a measuring instrument for detecting and measuring the intensity and direction and duration of movements of the ground (as an earthquake)
- Seismograph needles, the world over, jumped wildly a fortnight ago.
- In the Benioff seismograph, earth movements are magnified 200,000 times.
- This involves setting off charges of dynamite, measuring the time required for the earth ripples to reach a seismograph planted some distance away, studying the wavy lines on .