Holtz-type influence machine

Holtz-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.
This influence machine has the design features of Wilhelm Holtz of Germany (1836-1913). There are two glass discs, one fixed and the other rotating. The fixed disc has two oblong holes called windows, each with a paper contact or “sector” held onto the glass with varnish. The slightly smaller rotating plate is turned by the user with a crank and spins close to the fixed plate, charging as it spins. Two brass combs mounted on the glass stands gather the charge and conducted it to a Leyden jar. When using the Holtz design one needed to “prime” the machine by putting a charge on one of the sectors and then connecting the electrodes to begin building up the charge. The brass bar attached to the axle is called the neutralizer bar and prevents the charging action from reversing at the wrong time and discharging the machine. The rubber disc under the fixed plate is stamped: "Ed Borchardt / Berlin / 400" and may be a maker’s mark.
This object was repaired in late 1958. The parts replaced included the rotating plate, the stationary plate clamp and screw, rotating plate drive handle, drive belt for rotating plate, and one Leyden jar.
Location
Currently not on view
Object Name
influence machine
electrostatic generator
date made
ca 1890
Measurements
overall: 26 in x 32 1/4 in x 25 in; 66.04 cm x 81.915 cm x 63.5 cm
ID Number
EM.311762
catalog number
311762
accession number
152769
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Work and Industry: Electricity
Science & Mathematics
Data Source
National Museum of American History
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