Hi Geoff,

I'm not sure, but I think the suggested design might suffer from lack 
of sensitivity.  Simply having a long natural period doesn't, by 
itself, necessarily make for a good seismometer.

For example, consider a horizontal design made from a large metal 
disk which has a horizontal axle in a frictionless bearing.  Add a 
weight of a few grams on its rim and the disk will slowly rotate to 
have the weight move towards the bottom.  It will also act as a 
pendulum and will oscillate with a very long period.  But if you go 
through all the math, it turns out that it will have very little 
sensitivity to horizontal ground motions.  Long period alone doesn't 
equal a good seismo.  I think the proposed vertical design is also 
trading sensitivity for long period.

Regards,
Brett

At 01:14 PM 11/21/2010, you wrote:
>
>
>I have been looking at gravity normalized to 1G
>for various periods of a pendulum and come up with
>the following Idea.
>
>Given: 1g and 1sec period (P)
>Find: new values of g for any given period.
>
>g = 1 / P^2
>
>This means if you could float lead in some kind of
>dense fluid which through buoyancy removes
>94% of its weight you might get a 5 second period
>by then suspending the submerged piece of lead
>by a spring extended by what might be
>10 inches or so of extension from zero.
>I have not tried this, possibly one of you know more ?
>What fluid is dense enough to take up the weight
>of lead which is like 11.4 grams/ml
>you need a fluid with a density of like
>11.4 * .94 or 10.72 grams / ml.
>I can find no such fluid, but is there a way
>to create such a fluid of practically any
>density you might need ?
>
>I figure anything which can counter 94% the mass weight
>will give the same result. Not just fluids.
>
>Am I wrong here ?
>
>http://www.1goss.com/Arkansas42.jpg
>
>Comments Please, private or public welcomed.
>
>geoff


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