Setting up a Paraconical Pendulum in a Concrete Building

Here are the illustrations showing how a paraconical pendulum may be set up through a hole in a concrete floor. This pendulum is our prototype which we showed at the SSE conference in Las Vegas in May 2004, and it is not quite the same as the pendulums we are actually using currently.

First we see a disused shelf, to which we are going to mount the pendulum. You should imagine that this is actually a floor of a concrete building (with a friendly owner), perhaps about 30 cm thick. It is obviously necessary to be able to access both the room over this floor (the "upper room"), and the room underneath it (the "lower room").

Then we place the L-shaped support member, already bolted to its support bars, on the shelf (in imagination, the concrete floor) in the desired place, in order to mark up the positions of the one large and four small holes we are going to drill and cut.

This picture shows the support members with the bolts inserted into their four end holes (but not secured). With an actual concrete structure, we would mark the concrete underneath these holes, and we would drill long holes with a masonry drill, bigger than 12mm which is the size of the bolts we will use.

Then, having marked the size we want, we remove the aluminum members and cut the big hole for the pendulum rod and ring. In the real case with a concrete floor, we would need to use a pneumatic drill or other suitable violence to get this hole through... You can see the four small bolt holes and the one large pendulum hole.

Then we put the support members, still bolted together to preserve their correct alignment, back over the hole, as seen below, and (in this case) we tighten up the bolts, or (in the real case) we pour epoxy resin or concrete into the four small fixing holes, so as to set the bolts tightly in them.

After this, we can remove the L-shaped support member, leaving the two bars securely in place in the correct alignment. Then we can put it back while fitting the paraconical pendulum, in all its glory. This was a two-handed job, so I took no particular photos of the procedure, which in any case is straightforward. The paraconical pendulum all set up looks like this:

As you can see, the suspension of the pendulum, i.e. the support ball and flat, are accessed via the upper floor of the building, while the bob is accessed from the lower floor.

Here is a closeup of the ring (this is the view when you are on the upper floor). By the way, in the real case, we have found that the use of wing nuts is not to be recommended: simple hex nuts are better.

And here is a closeup of the ball and the flat. Why didn't Allais take some decent photos like this? (This flat is an obsolete version, no longer in use for the production pendulums.)

And here is a photo of the bob, shown while it is being pulled sideways by a thread, ready for being released. This is a very crude realization of this procedure; in the actual case it is done much more scientifically, as shown elsewhere on this site. (And I don't claim that my release procedure is the last word on the subject!)

And here is a general view of the pendulum as seen from below (this is the view when you are on the lower floor):

The normal operations of swinging the paraconical pendulum and measuring its azimuth and amplitude of swing are of course performed upon the lower floor, while operations such as centering the support ball upon the flat, changing the support ball and/or flat, etc. are performed upon the upper floor.


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