Joseph Priestley Static
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An electric machine consists of
the combination of two materials, which when rubbed together produce
static electricity, and of a third material or object which acts as a
collector for the charges.
The first devices for producing
electricity were very simple. The ancient Greeks discovered the strange
effects of amber rubbed with fur and other material. In the 17th
century, scientists used sticks of resin or sealing wax, glass tubes and
other objects. By the time of Benjamin
Franklin (Franklin became interested in electricity about 1745)
large glass tubes about three feet long and from an inch to an inch and
a half in diameter were popular; these were rubbed either with a dry
hand or with brown paper dried at the fire.
There are two major categories of
electrical machines: Friction and Influence. A friction machine
generates static electricity by direct physical contact; the glass
sphere, cylinder or plate is rubbed by a pad as it passes by. Influence
machines, on the other hand, have no physical contact. The charge is
produced by inductance, usually between two or more glass plates.
All through the 18th and 19th centuries there was
tremendous interest in electricity. Scientists such as
made major advances. Prior to Faraday's invention of the induction coil
in 1831 however, the only way to generate high voltage electricity was
via a static generator such as these.
Rotating the wheel created a static
charge, which was available on the "prime collector" (the brass ball or
cylinder at the top or front of the device). The charge could then be
stored in a Leyden jar or measured by an
History of the Electrical Machine
Go to the next page for a detailed
history of electrical machines.
Below are some examples of the electrical
machines in my collection: