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From: guy@slu70.UUCP
Newsgroups: net.physics
Subject: Re: Electric Brae
Message-ID: <162@slu70.UUCP>
Date: Thu, 20-Feb-86 13:33:46 EST
Article-I.D.: slu70.162
Posted: Thu Feb 20 13:33:46 1986
Date-Received: Mon, 24-Feb-86 08:09:12 EST
References: <736@brl-smoke.ARPA> <933@nmtvax.UUCP> <571@jplgodo.UUCP>
Distribution: net
Organization: Saint Louis University, St. Louis, MO
Lines: 29
Summary: gravity

In article <571@jplgodo.UUCP>, steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224) writes:
> then the use of a spirit level at the location of interest would only *prove*
> that gravity was not pulling in the *right* direction.  Rather, what is needed
> in this case is to measure the slope of the ground or whatever from a location
> where everyone agrees that the direction of the gravitational pull is OK.
> Possibly a surveyor or a civil engineer could explain how this might be done.
> Are the any such out there reading this?

This could be quite easily done with a level (a surveying instrument with a
telescope that sights a level line). Just back off far enough to get out of
the immediate vicinity. I've made shots of this sort at a distance of a
quarter mile as long as there aren't too many heat waves. It's not hard to
get accuracy in the hundredth of a foot range. If the anamoly were of a large
scale this wouldn't work however as the level uses the direction of gravity
as a reference. In this case you could try triangulating and see if the angles
add up right. If gravity is significantly off vertical you will, in effect
be surveying on a curved surface and a triangle will not add up to one hundred
eighty degrees. You can also refer yourself to fixed stars. Putting on my
geophysicists cap, you can also do a gravity survey across the site. Gravity
meters measure the magnitude of the field and should show the presence of
any subtantial anomaly. As far as whether such an anomaly is likely to exist,
I should point out that gravity anomalies (due to ore bodies and such) are
so small that there is no detectable deflection of the direction of the field.
In order to produce effects of the magnitude described, you'd have to have
a small deposit of something like neutronium just below the surface, not
a very likely proposition.

                                              Guy M. Smith
                                   (your friendly neighborhood paleomagnetist)