during the busy hours of the
day. As an instance of what can be done, 150 words per minute have
been dictated in Paris and transcribed in London by shorthand writing.
Thus in three minutes 450 words were recorded, which at 8 s. cost five
words for a penny.

5. _Difficulties._--The difficulties met with in long-distance
speaking are several, and they may be divided into (a) those due to
external disturbances and (b) those due to internal opposition.

(_a._) Every current rising and falling in the neighborhood of a
telephone line within a region, say, of 100 yards, whether the wire
conveying it be underground or overground, induces in the telephone
circuit another current, producing in the telephone a sound which
disturbs speech, and if the neighboring wires are numerous and busy,
as they are on our roads and railways, these sounds became confusing,
noisy, and ultimately entirely preventive of speech. This disturbance
is, however, completely removed by forming the telephone circuit of
two wires placed as near to each other as possible, and twisted around
each other without touching, so as to maintain the mean average
distance of each wire from surrounding conductors the same everywhere.
Thus similar currents are induced in each of the two wires, but being
opposite in direction, as far as the circuit is concerned, they
neutralize each other, and the circuit, therefore, becomes quite
silent.

In England we make the two wires revolve completely round each other
in every four poles, but in France it is done in every six poles. The
reason for the change is the fact that in the English plan the actual
crossing of the wires takes place in the span between the poles, while
in the French plan it takes place at the poles. This is supposed to
reduce the liability of the wires to be thrown into contact with each
other by the wind, but, on the other hand, it diminishes the
geometrical symmetry of the wires--so very essential to insure
silence. As a matter of fact, contacts do not occur on well
constructed lines, and I think our English wires, being more
symmetrical, are freer from external disturbance than those in France.

[Illustration: FIG. 1.]

(_b._) The internal opposition arises from the resistance, R, the
capacity, K, and the electromagnetic inertia, L, of the circuit. A
current of electricity takes time to rise to its maximum strength and
time to fall back again to zero. Every circuit has what is called its
time cons