Plate-type influence machine

Plate-type influence machine

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Description (Brief)
People from ancient times knew that rubbing certain materials and then touching something caused a spark. Studying what is called electrostatics laid the groundwork for understanding electricity and magnetism. Natural philosophers, scientists, and instrument makers created many ingenious devices to generate electrostatic charges starting in the 1600s. These machines varied in size and technique but all involved rotary motion to generate a charge, and a means of transferring the charge to a storage device for use.
Many early electrostatic machines generated a charge by friction. In the later 19th century several designs were introduced based on induction. Electrostatic induction occurs when one charged body (such as a glass disc) causes another body (another disc) that is close but not touching to become charged. The first glass disc is said to influence the second disc so these generators came to be called influence machines.
Sometimes laboratory researchers buy equipment from instrument makers and sometimes they make equipment themselves. This two-plate machine has no maker’s marks and may have been made at Columbia University, perhaps for experimental purposes since it is unlike other machines in the collection. The glass discs rotate in opposite directions when the user turns the crank. The discs have no windows as in a Holtz machine or surface contacts as in a Toepler machine. Each plate is swept by two brass brushes and there is an electrode on each side of the machine that sits between the two plates. One electrode is mounted on an arm that is insulated from the rest of the machine and the other is mounted on an arm that attaches to an empty socket outside the frame. Presumably the socket held a discharger or other device that is now missing.
Location
Currently not on view
Object Name
influence machine
electrostatic generator
Other Terms
electrostatic generator; Electrostatic Devices
Measurements
overall: 24 in x 29 1/2 in x 14 1/4 in; 60.96 cm x 74.93 cm x 36.195 cm
ID Number
EM.322919
catalog number
322919
accession number
249200
Credit Line
from Columbia University, Department of Physics, thru Alvin P. Tramm
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Work and Industry: Electricity
Science & Mathematics
Data Source
National Museum of American History
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