PSN-L Email List Message

Subject: Re: Folded pendulum history
From: John or Jan Lahr johnjan@........
Date: Mon, 31 Mar 2003 22:44:39 -0700

Hi Dave,

Thanks for finding this information!  What do you think we should call this
type of system?  How about "Ewing duplex-pendulum seismometer?"


At 03:20 PM 3/31/2003, you wrote:
>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" 
>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,
>Public Seismic Network Mailing List (PSN-L)
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