The Experimental and Historical Foundations of Electricity - Unicamp

electricity. Initially he built a metal versorium, but later on he noticed that, for
his purposes, it would be better to have versoria made of glass or wax. He then
described an experiment analogous to Experiment 5.18: 9
There is still another very simple way to know the kind of electricity
of a body for which this virtue is very weak [...] For the time being I
will avoid [presenting] the reader with the tiresome and discouraging
details of the faulty or imperfect experiments, and I will only say
that in order to succeed, it is necessary to utilize a glass needle [a
versorium made of glass] placed above a very long glass pivot, this
needle should have in one of its ends a hollow metal ball, and in
the other [end] a counter-weight of glass, it is necessary to dry all
its portions, and then it is necessary to communicate the electricity
to the metal ball with a [rubbed glass] tube, or of any analogous
matter, the [charged] ball will be then attracted by bodies which
have a resinous electricity, and will be repelled by the bodies which
have a vitreous electricity.
5.4 The Triboelectric Series
In this experiment we illustrate how the practical procedure of Experiment
5.14 can be utilized with a wide variety of substances rubbed against different
materials. A metal versorium will be utilized to test whether the body is neutral
orcharged. Initiallywetouchtheversoriumwithourfinger,inordertodischarge
it. We then slowly move the body near the versorium, without touching it.
When the versorium remains at rest, without being oriented toward the body,
we say the body is neutral. When the versorium is oriented toward the body,
we say the body is charged.
In order to test the charge acquired by rubbed bodies, we utilize two electric
pendulumschargedwithoppositeelectricities. Thesetwopendulumsarekeptat
a good distance from one another on the table. Before charging the pendulums
we touch the paper disk of each one of them with our finger. We then charge
them by contact. A simple and efficient procedure is to rub a plastic straw
and bring it close to one of the pendulums. The paper disk is attracted by the
rubbed straw, touches it, and is then repelled by it, as it acquires a charge of
the same sign.
From our experience with this kind of experiment, we know that it is easy to
charge a pendulum negatively. After all, a plastic straw acquires a large amount
9 [DF33b, pp. 473-474]: “Il y a encore un moyen bien simple pour connoitre le genre
d’électricité d’un corps dans lequel cette vertu est très-faible [...] J’épargnerai cependant au
lecteur un détail ennuyeux & rebutant d’expériences manquées ou imparfaites, & je dirai
seulement que pour réussir, il faut se servir d’une aiguille de verre posée sur un pivot de
verre très-long, que cette aiguille porte à l’un de ses bouts une boule de métal creuse, & à
l’autre un contre-poids de verre, qu’il faut bien sécher toutes ces piéces, & qu’alors il faut
communiquer l’électricité à la boule de métal avec le tube, ou quelqu’autre matiére analogue,
la boule sera alors attirée par les corps dont l’électricité est résineuse, & repoussée par ceux
qui ont l’électricité vitrée.”
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