Curiosity at the US Geological Survey

The American Red Cross Blood Drive was held this morning at the headquarters building of the US Geological Survey,  just a very short distance  from us here in Reston.    It was an interesting building with many maps and satellite images on display.    There is a Visitors Centre which is now only occasionally open due to budget cuts but also geological and nature trails in the grounds (too cold for that this morning at -6 with a strong wind making it feel much colder than that).  

This curious object in a display case caught my eye - initially looking like a rather ornate punch bowl!  It was, I think, made of metal with little china frog cups around it.

As the little card next to it explains,  the object is a seismoscope used in Imperial China before modern instruments were available for detecting earthquakes.  This seismoscope was able to predict the direction in which an earthquake had occurred.

The principle is that the seismic energy waves vibrate the bowl which is filled with thick liquid, a large ball and a number of small balls.  The large ball moves along with the energy waves, knocking the small balls from in front of it, the small balls then drop out of the mouths of the dragons and into the mouths of the frogs below.  The direction of the earthquake is 180 degrees from where the balls drop out.

The card indicates that once the direction was determined, Emperors would send caravans of rescue supplies to assist those affected by the earthquake.

Adjacent to the seat where I was greeting the blood donors today was an audio visual display about the San Andreas fault with eye witness accounts and images of the San Francisco earthquake.  Having watched and listened to it on continuous loop for a number of hours it will be food for thought when we visit there in a couple of weeks...