Benjamin Franklin
Benjamin Franklin (1706-1790) was not only a scientist but also an engineer. More than a decade before James Watt invented his improved steam engine and launched the industrial revolution in England, Benjamin Franklin devised a working electric motor.
Electrical technology in Franklin's day consisted mainly of scientific
instruments. By 1745, electrical scientists exploring the nature of the
"sublime fluid" had developed crude electrostatic generators and
an early form of the capacitor, which they called the "Leyden
jar." Experimenters employed these new devices to explore how electricity
could be generated, stored and transmitted but made little practical
application of their knowledge.
Franklin developed an interest in electricity in 1747 after receiving an
"electric tube" from a friend. Over the next few years, he conducted
experiments sporadically and collected examples of the latest electrical
instruments. Like other scientists, he explored the ability of various
materials to accumulate charges and the curious attractions or repulsions these
charged bodies had for each other. However, he also sought more productive use
of his findings.
In 1748, he invented the "electric wheel." Franklin's machine
consisted of a vertical shaft that was free to rotate, from which several glass
bars extended like spokes. Each bar was tipped with a brass thimble. Placing
the terminal of a "negatively charged" (as Franklin understood it)
Leyden jar near the wheel allowed the thimble/glass assemblies to act as
capacitors; as each assembly charged up, it tended to be repelled from the
Leyden jar. A second, "positively charged" jar set nearby had the
opposite effect, pulling the spokes toward it. The result was that the wheel
would begin to rotate, and it would remain in motion until the charges on the
Leyden jars dissipated.
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| Franklin's Electric Motor |
Unfortunately, the motor was only strong enough to continue turning at 12
to 15 rpm when loaded with 100 Spanish dollars. Franklin probably suspected
that even a full-scale version of his electrostatic motor could not compete
with steam engines or water wheels as a practical source of power for industry,
though he did suggest it could be used to power a turkey rotisserie. A few
others tried to put the wheel to work, including an unknown toymaker who
constructed a small, motorized carousel in about 1830 (an example of which
resides in the Bakken Museum and Library). Described in Franklin's
well-received 1751 book on electricity, the wheel was overshadowed by his other
findings, including his famous proposal to use lighting rods to protect houses
from damage.
Later practitioners found little use for the electrostatic devices
invented in the late 18th century. According to historian Michael Schiffer, the
invention of the voltaic pile (an early form of battery) in 1800
dampened enthusiasm for electrostatic generators, while the development of the
electromagnetic motor by Michael Faraday and others a few years later
permanently turned the course of electric motor development away from machines
like Franklin's. Thus, Franklin’s electric wheel has faded into obscurity.