n all 70 pounds.
A small alternator of 200 watts and 100 volts is coupled direct to the
aeroplane motor, a new clutch coupler being employed for this purpose.
By means of a small transformer the voltage is raised to 30,000 volts,
at which the condenser is charged. In this instance the musical spark
method is employed.

The whole of the high tension wiring is placed within a small space
so as not to endanger the pilot, while the transformer is hermetically
sealed in a box with paraffin. The aerial comprises a trailing wire 100
feet in length, which, however, can be wound in upon its reel within 15
seconds. This reeled antenna, moreover, is fitted with a safety device
whereby the wire can be cut adrift in the event of an accident befalling
the aeroplane and necessitating an abrupt descent. With this apparatus
the French authorities have been able to maintain communication over a
distance of 30 miles.

In maintaining ethereal communication with aeroplanes, however, a
portable or mobile station upon the ground is requisite, and this
station must be within the radius of the aerial transmitter, if
messages are to be received from aloft with any degree of accuracy and
reliability. Thus it will be recognised that the land station is as
important as the aeroplane equipment, and demands similar consideration.

A wide variety of systems have been employed to meet these conditions.
There is the travelling automobile station, in which the installation
is mounted upon a motor-car. In this instance the whole equipment is
carried upon a single vehicle, while the antenna is stowed upon the roof
and can be raised or lowered within a few seconds. If motor traction is
unavailable, then animal haulage may be employed, but in this instance
the installation is divided between two vehicles, one carrying the
transmitting and receiving apparatus and the generating plant, the other
the fuel supplies and the aerial, together with spare parts.

The motive power is supplied by a small air cooled petrol or gasoline
motor developing eight horse-power, and coupled direct to a 2-kilo watt
alternator. At one end of the shaft of the latter the disk discharger is
mounted, its function being to break up the train of waves into groups
of waves, so as to impart a musical sound to the note produced in the
receiver. A flexible cable transmits the electric current from the
generator to the wagon containing the instruments. The aerial is built
up of masts car