Globe-type Electrostatic 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.
This incomplete machine dates from about 1750 and appears to be Benjamin Franklin’s design. In the late 1740s, Franklin began investigating electricity with instruments supplied by friends in Britain. Scientific instruments of all types were in short supply in colonial America so Franklin supplemented his imported equipment with items of his own design. Early electrostatic machines generated a charge by spinning a globe against a pad. The charge could then be used directly in experiments or transferred from the globe to a Leyden jar. The hollow glass globe on this machine rubs against a leather pad seasoned with a specially formulated grease. The charge collector assembly, missing from this machine, consisted of brass pins that rode against the glass and carried the charge to a brass ball set on an insulating glass rod. Princeton University donated this machine in the 1960s and kept a second machine for display there. The exact origin of the two generators is uncertain but an oral tradition at Princeton associates both machines with Franklin.
Location
Currently not on view
date made
ca 1750
Physical Description
wood (overall material)
glass (globe material)
fiber (part material)
rubber (part material)
cloth (part material)
metal (part material)
Measurements
overall: 60 1/2 in x 30 in x 27 1/2 in; 153.67 cm x 76.2 cm x 69.85 cm
ID Number
EM.325513
catalog number
325513
accession number
2008.0088
Credit Line
from Princeton University, Department of Physics
subject
Science & Scientific Instruments
See more items in
Work and Industry: Electricity
Science & Mathematics
Artifact Walls exhibit
Electrostatic Machines
Energy & Power
Data Source
National Museum of American History, Kenneth E. Behring Center

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