> Jinx, could you please forward this to the list? thanks, Alice
>
> Geophysicists routinely use microgravity meters
>  to measure small changes in the earth's gravitational field.
> The popular ones use torision, a mass, and a spring.
>  These meters  usually only measure the vertical component of a
> gravitational field.  But they can be deflected, for example,
>  by the mass of a nearby mountain. In fact, it was awhile before
>  the height of Everest could be measured because it's so massive
>  it kept throwing off the plumb bobs the surveyors were using.
> I routinely see periodic changes in water levels in groundwater
>  wells/bores a thousand miles from the sea. These little
>  deflections are caused by the moon's tidal effect moving
>  the crust of the earth around, and alternately compressing
>  and dilating the aquifer.  Even big tropical storms change
> gravity by changing the pressure of air in the ground by unloading
> aquifers and allowing them to expand. This causes changes in the
> measurement
>  of gravity because it changes your distance from the center of the
> earth. Sheesh.  There's even a term, 'pneumatic
> impedance', describing the effect of changes in pore volume
>  within dirt that interrelates air pressure and pneumatic
>  conductance.  This determines the rate air can move underground.
>  This effect is enough to throw off a gravity measurement.
> So detecting gravity waves will involve eliminating an awful
>  lot of stuff and hoping what's left is what you are looking for.
>
> alice
>
>

>> And I think mining surveyors can detect ore deposits from the air
>> by some sort of trailing wire. Australia is interlaced with fault lines
>> that are used for both earthquake prediction and mineral location
>> by measuring the changes in magnetic fields as the plates move
>
>In all cases there is 'something' at the end of the trailing wire. The
>something is usually a magnetometer but in rare occasions there is also a
>gravimeter in the blob at the end of the cable.
>
>Peter
>
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