Hi Ted,

The sensor that you've designed will be sensitive to rotations of the 
ground with a vertical axis.  The problem is that such rotations are 
very small and thus difficult to detect.  This is a budding field of 
seismology.  See, for example:  http://pubs.usgs.gov/of/2007/1144/

Of course the inverted T will also swing like a normal pendulum with 
period determined by the overall length of the blade, unless it's 
constrained to remain vertical.

Cheers,
John

At 10:40 AM 12/15/2007, you wrote:

>Hi Folks,  This is an observation and a question.  I have an 
>Anniversary clock, perhaps also called a 500 day clock, as you only 
>need to wind it once a year, or so.   I know very little about 
>clocks, but have worked on a few clock movements and 
>escapements.   I have some old clocks which are 8 day movements.   I 
>wondered why the big difference in power consumptions, and spring 
>properties between the two types.
>
>The 8 day movements use a short pendulum which is maybe 1/2 second 
>natural period.  The anniversary clock has a short spring, instead 
>of a pendulum, which is  like a flat thread.  This spring is fixed 
>at the top and has four masses, brass balls on the free end.  One 
>period of this spring is about  8 seconds.   The mass in motion, 
>twist the thread like spring, until the power of the spring stops 
>the mass, and swings it in the opposite direction.  A different 
>coiled mainspring then add a kick to the mass and the cycle repeats.
>
>Always looking for different ways to obtain a 20 second period, I 
>took a band saw blade, cut it and suspended it from my shop 
>ceiling.  It now hangs similar to the thread like movement spring of 
>the anniversary clock.  At the bottom of the 72" band saw blade, I 
>attached a 36" yardstick.  This now looks like an inverted "T".   I 
>added a mass to both ends of the yardstick.  I twisted the spring 
>and released it.   I found it rotated back and forth and it period 
>was about 8 seconds.  I keep adding equal mass to both end of the 
>yardstick, and the period was 24 seconds.
>
>  The yardstick seems to always come to rest at the same point, as 
> the spring wants to untwist.
>
>My question:  Has anyone tried this approach?   If so,  could anyone 
>direct me to more information about it on the internet?
>
>Thanks, Ted


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