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Gravity detectors was Block in boat - OT, NO metal just brain
(Beecrofter) wrote in message . com...
These gravity anomalies are called "vertical deflections" and are the
places where the gravity vector differs from perpendicular to the
earths surface.
Over large iron deposits you will find them to be a bit larger but
they really don't follow the geomagnetic fields to any degree.
I believe they used to test for them with pendulous gyroscopic
acellerometers but I bet the new stuff is a bit more refined.
I have a book on the history of maps and mapmaking. It seems that
back in the 1600's there was a big discussion about how big a degree
was on the earth and the way they chose to measure this was discussed
greatly in this book. They took pendulum clocks, adjusted them to
great precision in France. They then disassembled them carefully,
loaded them on ships and sent them down closer to the equator, to use
in astronomical observatories. They found that the rate of the clock
changed. They correctly assumed that the gravitational field was
different at different places on the earth. I believe that these
clocks qualify as the first precision gravity meters.
We had the gravity constant checked at our laboratory in Houston. We
were using precision dead-weight testers to calibrate pressure gauges
(How precision? 0.1 psi resolution at 20,000 psi static). A shaky old
man in a baseball cap came in with a box about a foot cubed with a
battery pack attached. He set the box on our bench, stared through an
eyepiece, and said it had not stabilized yet. He said he would be
back later, and disappeared for an hour. Then he came in and read the
gravity constant at our location. I think the box had nothing more
precise than a weight with a spring on it, and a scale read with a
microscope. The precision, and stability, came from maintaining a
VERY precise temperature in the box. I.e., the wait for the box to
stabilize better was a wait for the temperature to stabilize.
In summary, "gravity meters" have been around a long time, and don't
require rocket-science to build.
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