| Franklin's Pane is a parallel-plate capacitor made
of a pair of metal-foil plates glued to the surface of a glass plate. It
is electrically the same as the Leiden
Jar, but has a more useful geometry. The flat version of the Leiden
jar was developed ca. 1750 by Benjamin Franklin (1706-1790). In this form
it was sometimes called a Fulminating Pane.
The Pane is charged by connecting one foil to the prime conductor of an electrostatic machine, and grounding the other foil.
The nineteenth century mind turned the pane into a shocking practical joke. The pane was held in a decorative wooden frame, and a picture on a piece of paper was pasted over the foil. The "picture" was laid flat on the table, the lower side grounded, and a coin placed on top of the picture. The unwary victim leaned over to pick up the coin, and got a nasty shock. There must be some sort of moral lesson here.
This example of Franklin's Pane is in the collection of historical physics instruments at Yale University.
Franklin's Pane can also be made into an oscillator:
"If the glass plate coated with tinfoil is charged, and
then placed upright on a stand, it may be slowly discharged by placing
a bent wire on the edge with the extremities covered with pith balls. The
wire balances itself, and continues to oscillate with noise until the electricities
of the two surfaces neutralize each other."
This version of Franklin's Pane is in the collection of
historical physics instruments at Yale University.