metal spheres pass close to electrodes mounted at either
side. One electrode is connected to your generator, and
the other to ground.
Though the motor is not usually self-starting (mine
has been for some odd reason), given a gentle push it
will quickly spin up to high speed. Charges on the
positive electrode are attracted to the grounded
electrode and move the wheel at often remarkable
speeds. It’s worth noting that Franklin motors have been
made self-starting by adding a small ion motor to the
A Leyden Jar
You can greatly increase the power of your Van de
Graaff by storing its output in a large capacitor. Figure 8
shows a five gallon bucket configured as a leyden jar.
Construction is straightforward. Wrap aluminum foil
around the outside and bottom of the bucket (as shown)
and hold it in place with tape or contact cement. Do the
same on the inside. A brass drawer pull on the lid is
attached to a chain. The chain makes contact between
the drawer pull and the foil inside.
When the lid is placed on the bucket, the outside foil
should be connected to ground, and the drawer pull
■ FIGURE 8.
connected to the top of your Van de Graaff. After
running your generator for a few minutes, the leyden jar
will hold a large charge. To demonstrate this charge, you
can short the drawer pull to ground with a discharge
pole. Figure 9 shows a simple discharge pole. A heavy
bare wire is attached to the end of a length of PVC pipe
as shown. This allows you to stand some distance from
the leyden jar holding only the plastic handle, and
allowing the metal wire to short the connection between
the drawer pull and the side of the jar.
The result will be a thick bright spark and a very loud
CRACK. The leyden jar makes many higher energy
Note: Never — under any circumstances — touch a
leyden jar without making certain it is fully discharged
in this manner. Even if it is not connected to your Van
de Graaff, leyden jars have been known to pick up a
charge in proximity.
Halloween Magic Ideas
I’ve seen a very long string of freaky things happen
when running my Van de Graaff, and you’ll discover
these as you experiment. A number of great Halloween
door tricks suggest themselves immediately.
■ FIGURE 9.