Vol. 17: The Wimshurst Influence Machine

When assembling a proper laboratory, the gentleman or lady experimenter should be sure to include a Wimshurst electrostatic generating machine.

By Jake von Slatt

Photos by Jake von Slatt

Illustrations by Damien Scogin

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Wimshurst Inflluence Machine:
Building Franklin's Bells
By Jake von Slatt

One popular demonstration of electrostatic charge is known as Franklin's Bells. Franklin's Bells are just that, a pair of metal bells, mounted on insulating supports, with a wooden or pith ball suspended from a thread between them. When the bells are connected to a source of electrical charge such as a Wimshurst influence machine, the wooden ball is attracted to one of the bells. When the ball strikes the bell, it acquires a like charge from the bell, and is then repelled, swinging to the other bell, where the process is repeated, resulting in a prolonged ding-ding-ding-ding for as long as the charge persists.

Now, ol' Ben Franklin did not have a Wimshurst machine - they were invented about 100 years after he performed his experiments. What Franklin did was connect one of the bells to a lightning rod on top of his house and the other to ground - extremely dangerous! - so that when an electrical storm moved into the area, the bells would ring and alert him to gather his kite flying gear!

The above set of Franklin's Bells was made from a simple wooden base, 3 sections of 3/8" fiberglass rod, and 2 brass bells from an old desktop telephone. The "clapper" is a wooden bead strung on a length of upholstery thread, attached by a clothespin.

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