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Electrostatic Merry-go-round
French? circa 1830
This merry-go-round is an electrostatic motor of a type invented by Benjamin Franklin. Static electricity of opposite polarities would be connected to the two brass balls atop the glass pillars. The merry-go-round spins easily on a pivot point in the center. There is a small ivory piece at the end of each arm of the merry-go-round. You start the merry-go-round spinning by hand. When an ivory piece approaches a brass ball, it takes on the electric charge from that ball. It's then repelled, so the spin gets a little "kick" as the ivory goes past the ball. When that bit of ivory reaches the next ball, it is attracted (because it has an opposite charge from the opposite ball). But when it reaches that brass ball, it takes on that charge and is repelled. The result is a tug towards the ball as the ivory is approaching, and a push away from the ball as it leaves. The merry-go-round speeds up just a bit. It will keep spinning as long as the static electricity is applied. These motors often used Leyden Jars, to keep them spinning for quite a long time. Below is an example, extracted from Jacquet de Malzet's 1775 Précis de l'électricité:
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