PSN-L Email List Message

Subject: Re: Lehman??
From: CapAAVSO@.......
Date: Thu, 12 Jul 2001 08:32:47 EDT

In a message dated 7/12/01 12:27:44 AM GMT Daylight Time, 
tedr@.................. writes:

<< There was also a complicated mechanism between the end of the arm and the 
stylus, time did not allow me time to work out what did but it obviously had 
a use.
 The question I ask is: was it a Lehman and if so why hang the mass half way 
along and below the beam? Is it to magnify the amount the weight apparently 
moves??? And how were the oscillations damped, if indeed they were. >>

Hello Ted,

My first seismograph recorded with pen and ink on paper. I consider this now 
obsolete recording method much more satisfying than writing with an electron 
beam on a computer monitor, which I now do. I am therefore very interested in 
the museum's ink on paper seismograph and here are my best guesses as to how 
it works:

1)  No, I don't think it's a Lehman. What you see as a Lehman boom is 
probably a support arm for a 12-inch long hanging-mass pendulum swinging from 
half way out on the support arm.  

2) You describe what looked like: "a complicated mechanism between the end of 
the arm and the stylus". My guesss is this is a mechanical amplifier, a 
system of levers that causes the pen to move much farther than the amount the 
Earth moves in relation to the suspended mass, when the device records an 

3)  A careful designer could design such a system of levers to give perhaps 
anywhere from 20 to 50 X magnification of actual Earth movement due to an 
earthquake. With such a mechanical advantage the pen itself sliding on the 
paper would probably provide sufficient damping.

In a later posting, Chris Chapman says: "I live 50 miles away, but I plan to 
visit it in the next two months, if that is any help." I hope Chris will take 
a camera along and talk nice to the museum director so he will be allowed to 
take some close-up pictures of the "complicated mechanism" so we can figure 
out what it does and how it does it.

Best regards,

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Larry Cochrane <cochrane@..............>