Old Seismograph

I spent the afternoon at USGS to listen to a presentation on San Francisco's urban resilience initiative. Fascinating presentations.

On my way out I snapped a picture of this old seismograph. This machine was used to record earthquake ground-motions. The first seismographs work essentially by attaching a pen to a hanging mass, which stays stationary during an earthquake, while the paper underneath moves along with the ground. Nowadays, electronic seismographs are used.