I did run into these experiments before and the solution to the problem
probably lies in the like electrical charge of the two bobs, or some
other fairly common phenomenon.
The site I looked at said the same. Two bobs in an oil tank next to each
other.
The revission of the experiment was two bobs in separate oil tanks about
a mile appart with even greater angular difference. The revission might
take the like charge out of the picture. On the other hand, along the
same line of reasoning, the people quarter of the globe away from the
experiment should fall off the earth.
In that istance, a piano wire was used. No matter what the bobs might be
made off, the wires themselves would introduce thermocouple current with
its magnetic field. There is the unavoidable possibility that the first
experiment was also influenced by a like charge, and the revission by
another phenomena, i.e. magnetism or local gravitational anomaly.
By the way, there would also be the centrifugal force of the earth spinn
to be accounted for as well as the south north orientation in the case
of the revission.
There are way too many influences, which are not mentioned to be taken
into account.
If the centre of gravity lied on a sphere, its geometry would stil be
strictly centripetal. You can draw this in two D on paper.
This means that we are dealing with either a known phenomena, or an
unknown one, or a combination of a few, but the gravity is not likely to
be involved as the sole force.
Regards Slavek.