PSN-L Email List Message

Subject: Folded pendulum history
From: "David H. Youden" dyouden@.........
Date: Mon, 31 Mar 2003 17:20:58 -0500


I have finally hit pay dirt in my quest for the original folded pendulum 

The original instrument of this type was built in 1882 by Dr James Ewing. I 
believe that Dr Ewing was in Tokyo at the time. His instrument used a 
common pendulum coupled to an inverted pendulum so as to decrease the 
stability of the common pendulum. It appears to me that this was a two-axis 
instrument. Dr Ewing referred to it as a "Duplex pendulum" seismometer.

History has it that a number, possibly ten of these instruments were placed 
at sites in Northern California and Nevada during 1887-1888. Seismographic 
observatories at Berkeley and Mount Hamilton had duplex pendulum seismometers.

Perhaps an avid researcher in California might be able to actually find one 
of these instruments.

Dr Ewing built many different seismometers and, along with Dr Thomas Gray, 
He seems to have been one of the founders of modern seismological 

The single axis instrument which I constructed is certainly not identical 
to the two-axis unit of Ewing, but it employs the same principals and is, 
in many ways similar to his duplex pendulum design.

My best to all,


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