The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

DISTRIBUTION OF ELECTRICITY. 65
project from its side, as in the machine shown in the figure.
The negative conductor supports the rubber, and receives from
it the negative electricity, not by induction, as is the case with
the positive conductor, but by communication. If it be required to accumulate positive electricity, a chain must be carried from the negative conductor (which of course is insulated)
to the ground. If on the other hand, negative electricity be
required, then the conductor must be put in communication
with the earth, and the rubber insulated.
The plate electrical machine is shown in fig. 4. It consists
of a circular plate of thick glass, revolving vertically by means
of a winch between two uprights: two pairs of rubbers, formed
of slips of elastic wood, covered with leather, and furnished
with silk flaps, are placed at two equi-distant portions of the
plate, on which their pressure may be increased or diminished
by means of brass screws. The prime conductor consists of
hollow brass, supported horizontally from one of the uprights; its arms, where they approach the plate, being furnished
with points.
With respect to the merits of these two forms of the electrical machine, it is difficult to decide to which to give the preference. For an equal surface of glass, the plate appears to be
the most powerful; it is not, however, so easily arranged for
negative electricity, in consequence of the uninsulated state
of the rubbers, though several ingenious methods of obviating
this inconvenience have been lately devised.
DISTRIBUTION OF ELECTRICITY.
When a substance be- Fig. 5.
comes charged with electricity, it is extremely
probable, in the opinion
of philosophers, that the
fluid is confined to its
surface, or, at any rate,
that it does not penetrate
into the mass to any extent. This is a question difficult to
demonstrate, and my observations have induced me to believe,
that in the case of voltaic currents the electricity moves upon
or at the surface, but that the interior of the metallic conductor
is under the influence of the fluid, though in a state of rest.
Experiments have been made with static or frictional electricity by Biot, and the following facts were arrived at A ball
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