lectricity is passed
over a conducting line to a distant station, where it is either directly
utilized for the purpose of lighting, heating, chemical decomposition,
etc., or indirectly utilized for the purpose of obtaining mechanical
power for driving machinery, by passing it through an electric motor.
The electric transmission of power has been successfully made in
California over a distance of some 220 miles, at a pressure on
transmission lines of 50,000 volts.

The high pressures required for the economical use of transmission lines
necessitates the employment of transformers at each end of the line;
namely, step-up transformers at the transmitting end, to raise the
voltage delivered by the generators, and step-down transformers, at the
receiving end, to lower it for use in the various translating devices.
These transformers are employed in connection with alternating-current
dynamos. Faraday not only gave to the world the first electric
generator, but also the first transformer, and one of the first electric
motors, and without these gifts the electric transmission of power over
long distances, which has justly been regarded as one of the most
marvellous achievements of our age, would have been an impossibility.

In high-tension circuits over which such pressures as 50,000 volts is
transmitted, no little difficulty is experienced from leakage and
consequent loss of energy. This leakage occurs both between the line
conductors and at the insulators placed on the pole lines forming the
line circuit. The insulators are made either of glass or porcelain, and
are of a peculiar form known as triple petticoat pattern. The loss on
such lines, due to leakage between wires, is greater than that which
takes place at the pole insulators, and is diminished by keeping the
circuit wires as far apart as possible.

In the early history of the art, electric transmission of power was
effected by means of direct-current generators and motors,--generators
and motors through which the current always passed in the same
direction. Such generators and motors, however, possessed inconveniences
that prevented extensive commercial transmission of power, since, as we
have seen, high pressure was necessary for efficiency in such
transmission, and the collecting-brushes and commutators employed in all
direct-current generators and motors to carry the current from the
machine or to the motor, were a constant source of trouble and danger.

When