Wimshurst-type influence machine
date: label: date made
content: ca 1925
notes: label: Description (Brief)
content: 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.
label: Description (Brief)
content: 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.
label: Description (Brief)
content: James Wimshurst (1832-1903) designed a new type of influence machine in the early 1880s. Since they did not need to be pre-charged or primed in order to work, they represented a vast improvement on previous machines. Within a few years Wimshurst became a generic term used to describe these devices and manufacturers began mass producing them at all price levels. This machine was used for many years to teach electrical science at Dunbar High School in Washington, D.C.
label: Description (Brief)
content: The machine features two plates made from hard rubber rather than glass that rotate in opposite directions. Each has 24 metallic wedges called sectors that interact to generate the high-voltage static charge, and each is swept by two brushes on a neutralizing bar. Two Leyden jars sit in cups on the decorated base along with the spark discharge rods. No circuit is under the base but the base itself is metal and so the jars may be connected in that manner. The machine reportedly produced sparks 2 or 3 inches (5 to 8 cm) long, depending upon humidity in the classroom. The unit is heavily worn from extensive use.
label: Location
content: Currently not on view
setName: label: See more items in
content: Work and Industry: Electricity
label: See more items in
content: Science & Mathematics
creditLine: label: Credit Line
content: from Dunbar High School, thru Charles Lofton
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.323732
label: catalog number
content: 323732
label: accession number
content: 252354
objectType: label: Object Name
content: electrostatic generator
label: Object Name
content: influence machine
physicalDescription: label: Measurements
content: overall: 11 1/4 in x 9 3/4 in x 7 in; 28.575 cm x 24.765 cm x 17.78 cm