Tracking down the origin of Arc plasma science. I. Early pulsed and oscillating discharges Page: 9 of 26
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is therefore between 125 J and 500 J if a charging voltage of 50 kV is assumed! For comparison, 40 J of
stored electrical energy are considered dangerous by today's safety standards .
Returning to the earlier, much smaller Leyden jars of 1746, Watson experienced the stored energy
when short-circuiting a jar with a wire: "the charged phial will explode with equal violence, if the hoop of
the wire be bent, so as to come near the coating of the phial..." ( p.117). Figure 4 shows a similar
experiment as described by the still young Alessandro Volta. With today's knowledge we can estimate that
the discharge current must have been high, the peak limited by the inductance of the circuit, and decaying
exponentially or, more likely, oscillating in the LC-circuit. Using the above formula one can estimate
C LI1 nF and Ec D1 J for early Leyden jars. The stored energy is still clearly below the hazardous
level, and some of the early reports on "terrible" experiences appear exaggerated but understandable
because the physiological effects were not anticipated.
In France, Jean Antoine Nollet (1700-1770), also known as Abbe Nollet, one of the most famous
and influential electricians, also experimented with Leyden jars, investigating the effects of electric shocks
on animals. Just months after Musschenbroeck's letter, he charged his jars to the limits of the dielectric
strength of the glass finding "bursting of the glass vessels by electric explosions. They [the glass vessels]
were pierced with round holes, three of four lines in diameter" (p. 126 ) (a line is the 12th part of an inch,
or 2.1 mm). Today's glass has breakdown strength of about 45 ky/mm. It can be assumed that glass of the
time contained more defects, which actually determine the breakdown strength. Timonthy Lane (1733/34-
1807), instrument maker at Knightsbridge near London, found that
"The quantity of electricity necessary to burst the phial, appears to vary more in
proportion to its thickness than its size; many phils of various sizes may be broken at 10 of the
electrometer, while others, nearly of thr same size, remain sound, with a stroke at 30, or even
more. I generally found green glass more difficult to break than white." 
A breakdown field strength of 10-20 ky/mm may be a good estimate, leading to 20-60 kV as the
maximum charging voltage of early Leyden jars.
Shortly after the discovery of the Leyden jar, many electricians used the discovery to perform
experiments on humans, animals, and the nature of electricity itself. Among them, besides
Musschenbroeck, Wilson, and Watson, were John Canton (1712-1772), Lord Charles Cavendish (son of the
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Anders, Andre. Tracking down the origin of Arc plasma science. I. Early pulsed and oscillating discharges, article, January 14, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc785933/m1/9/?q=leyden: accessed January 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.