PSN-L Email List Message

Subject: Re: Lehman??
From: CapAAVSO@.......
Date: Fri, 13 Jul 2001 09:15:38 EDT

In a message dated 7/13/01 2:50:44 AM GMT Daylight Time, ACole65464@....... 

<< I just scanned a small photograph out of an old catalog tilted "Geophysics 
 Geomagnetism", published by the Science Museum. The photo matches closely 
 instrument that you described in words. I picked a the copy of the catalog 
 when I was visiting London 10-12 years ago. Go to the following Web page to 
 see the scanned image (370K jpeg): >>

Thanks Allan,

Your very nice scanned image shows that it is a Lehman-type horizontal 
seismometer. The boom apparently extends back to a pivot point out of the 
picture with the mass supported by the turnbucle/cable going up at an angle. 
With the obviously very heavy mass stacked right up to the boom it would act 
like a Lehman seismometer. the photo shows two pins to restrain horizontal 
movement of the boom which extends into the complicated mechanism Ted 
describes. The mechanism looks like a system of compound levers that are a 
mechanical amplifier. I would guess that the nearest pen is amplified the 
least and records strong movement. What looks like two additional lever 
systems for the farthest pen probably amplify its movement additionally to 
show more detail in the seismogram. The pens and lever systems would provide 
drag that amounts to damping. Presumably the loop of paper runs for 24 hours 
so time could be measured from the start where the time of start would be 
marked on the paper loop. It is certainly an interesting mechanical device 
that could record earthquakes. Its sensitivity would depend on the lever 
system. The photograph shows what seems to be a carefully built and well 
designed system of levers that provide mechanical amplification. I hope Chris 
Chapman, who is an engineer, will figure out the amplification factor when he 
visits the museum in a couple of months.

Best regards,

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