by the camshaft which presses against the interruptor lever with the movable electrode on it until the latter makes contact with the fixed electrode and the circuit is then closed.

At the right instant the pressure on the movable electrode lever is released and a spring makes it snap back, thus wiping the fixed electrode and break

FIG. 25. THE MECHANISM OF THE WIPE SPARK IGNITER

A, Cross Section of the Wipe Spark Igniter. B, The Igniter Ready to Use.

ing the contact between them, and this makes a spark. An Otto igniter is shown at A and B in Fig. 25, and the mechanism working it is shown at A and B in Fig. 26.

Low Tension Magneto System.-A magneto electric machine, or just magneto for short, is a machine which generates electric alternating currents. There are two kinds of low tension magnetos made,

CYLINDER EXHAUST IGNITER

HEAD

LEVER LEVER

GAS COCK

GOVERNOR

FIG. 26. THE WIPE SPARK IGNITER ON AN OTTO ENGINE A, End View of Cylinder Head Showing Mechanism of Wipe Spark Igniter and Exhaust Valve. B, Side View of Cylinder Head Showing Mechanism of Wipe Spark Igniter and Governor Control of Gas Inlet Valve.

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and these are used for generating currents for wipe spark igniters, as they are far less troublesome than the battery and spark-coil system. Named, these two types of low tension magnetos are (1) the rotating magneto and (2) the oscillating magneto.

The Low Tension Rotating Magneto.-A magneto of this kind is built up of two main parts and these are (1) the field magnet and (2) the armature.

FIG. 27. THE LOW TENSION ROTATING ARMATURE MAGNETO A, Permanent Field Magnet. B, The Armature Core. C, Single Coil of Wire Wound on the Armature. D, The Magneto Complete.

The field magnet is merely a powerful, permanent horseshoe magnet, as shown at A in Fig. 27, and the armature is a cylinder of soft iron with grooves cut lengthwise in the opposite sides of it and having a shaft through it, as shown at B.

A single coil of fine insulated wire is wound in the grooves of the armature and the ends are connected to brass collector rings, called sliprings, on the shaft, see B and C, but which are insulated from it and from each other. The shaft sets in a pair of

bearings so that the armature can revolve freely between the poles of the magnet. A strip of copper, called a brush, presses on each one of the sliprings and a wire leads off from the fixed end of each one of the brushes, as at C. The magneto complete is shown at D.

If the armature is rapidly rotated low tension

ARMATURE
SPRING

SPRING

TRIP

A

FIG. 28-A. A Low TENSION OSCILLATING MAGNETO A, The Control Mechanism of a Low Tension Magneto.

electric currents will be set up in the coil of wire on it by the magnet and these will flow to the sliprings, where they will be taken off by the brushes; if now the ends of the wires are connected together low tension, that is, low pressure, currents will flow through the circuit thus formed, but when it is used to produce sparks the wires are connected to the fixed and movable electrodes.

The Low Tension Oscillating Magneto.—The term oscillating magneto means that the armature oscillates, that is, turns to and fro through a small arc instead of rotating continuously as in the magneto just described.

B

FIG. 28-B. A Low TENSION OSCILLATING MAGNETO
B, The Oscillating Magneto on a Gas Engine.

This rocking motion is accomplished by an arm that pushes the armature back a few degrees, when it is tripped by a lever and is then suddenly pulled around by a pair of powerful spiral springs. The whole scheme is shown at A and B in Fig. 28. This type of magneto is better than a rotating magneto only in that it is much easier to start the engine.