Electrical apparatus (electrostatic machine), before 1773
Photo courtesy of Constance...
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Photo courtesy of Constance V. Hershey

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Photo courtesy of Constance...
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The machine is an upright, open-frame wooden stand, supported on two legs with triangular bases. Three vertical stiles hold a horizontal framework within which is mounted, vertically, a globe of glass sandwiched between small turned wooden wheels. An iron rod passes horizontally through the wheels and the middle of the globe, holding it just above a small, rectangular wooden foot that can be brought into contact with the globe. The foot is now bare, but was formerly padded or covered, probably by a cloth or chamois pillow. Below the globe and its framework is mounted a large vertical wheel, which is/was connected to the globe's supports by a cord or band. The large wheel can be turned by a handle attached to the exterior. As it turns, the movement is transferred by means of the cord to one of the pair of small wheels attached to the globe. The small wheel spins, and the globe revolves. If the padded foot beneath the globe is raised to permit it to contact the globe, the resulting friction charges the air within the globe. Touching a metal rod to the surface of the globe draws off the charge, which can be stored or emitted as as a spark.

On a separate card at the foot of the device is printed: "Electrostatic machine made under the supervision of Benjamin Franklin. Used by Priestley." Joseph Priestley, the scientist responsible for discoveries related to the atmosphere, and for two works related to electricity, was an associate of Franklin's in England.

My thanks go to David Long, on the staff of Princeton's Firestone Library, who informed me of the existence of the electrostatic machine and facilitated my examination of it.
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