The Experimental and Historical Foundations of Electricity - Unicamp

attract either flame or bodies near flame; for such effluvia have the
virtue and analogy of rarefied humour, and they will produce their
effect, bringing about unition and continuity, not through the external
action of humours, or through heat, or through attenuation of
heated bodies, but through the attenuation of the humid substance
into its own specific effluvia. Yet they draw to themselves the smoke
from an extinguished candle; and the lighter the smoke becomes as
it ascends, the less strongly is it attracted, for substances that are
too rare do not suffer attraction.
From what has been seen before, not all substances are affected by rubbed
amber (or, at least, not all substances are attracted with the same strength).
Even some substances having the same weight and shape are clearly more
strongly attracted by a rubbed plastic than others. For example, equal threads
of cotton or copper feel a stronger attraction than threads of silk or synthetic
polyamide.
2.7 What Rubbed Substances Attract Light Bodies?
Experiment 2.11
We will now try to attract the small pieces of paper placed upon a table.
We bring several rubbed objects near the pieces of paper. We will rub these
objects in hair, in a sheet of paper, or in a cotton tissue. It is important to
have homogeneous objects, that is, objects made of a single material, in order
to avoid contradictory results. We should not, for instance, rub a plastic pen
with metal parts. In this case it is best to rub a plastic straw and a metal spoon
separately.
We list here some of these substances: plastic, amber, glass, wood, metal,
acrylic, a natural magnet, thin cardboard, rubber, etc.
When the precautions mentioned previously have been taken, what is normally
observed is that, after rubbing, amber, acrylic, and the plastic objects
attract the small pieces of paper, as in Experiment 2.1 (Figure 2.3).
All the other substances do not normally attract the pieces of paper, no
matter how long or how hard are they rubbed. This is represented in Figure
2.9 for a wood skewer.
In the case of glass there are exceptions, as there are several varieties of glass
with varying compositions and made by different fabrication processes. But in
general, after being rubbed, the most common glasses do not attract pieces of
paper. The same can be said of rubber, as there are several varieties of rubber.
The usual types of rubber found at home do not attract the pieces of paper.
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