remarks, which show the paradoxical nature of this concept if applied
to the hypothetical interior of the atom (Chapter IV). The quite
primitive phenomenon of electrical repulsion and attraction shows us
the same thing in a manner of which it is not difficult to form a
conception.

Modern physics itself, with the help of Faraday's field-concept,
describes these phenomena as caused by pressure - resulting from the
meeting in space of two similar electrical fields - and suction -
resulting from the meeting of two dissimilar fields. In the first case
the space between the two electrically charged bodies assumes a degree
of density, as if it were filled with some elastic material. In the
second instance the density of the space where the two fields
intermingle is lower than that of its surroundings. Here, clearly, we
have a state of negative density which acts on the electrically charged
bodies just as a lowering of pressure acts on a gas: in both cases
movement occurs in the direction leading from the higher to the lower
density. Electricity thus shows itself capable of producing both
gravity and levity effects, thereby once more confirming our picture of
it.

*

Our next task will be to examine the galvanic form of generating
electricity, in order to gain further light on our picture of the
electrical polarity.

Galvanism, as it became established through Volta's work, rests on
certain properties of the metallic substances of the earth. Compared
with the substances which may be used for producing electricity through