In both the magneto and the battery sides the spark is produced on the breaking of the circuit, and the coil is so arranged that by pressing a button when the switch is in the battery position, an intense vibrator spark is produced in the cylinder during that period when the circuit breaker is open, which will be the case during the first three-fourths of the power stroke. The current is transmitted to the distributor and passes through the spark plug of the cylinder that is on the power stroke. [Illustration: Fig. 115. Bosch Duplex Breaker. ] Should the engine come to a stop in such a position that the battery timer is closed, it will not be possible to produce a vibrator spark by the pressing of the button, but the releasing of the button will produce a single contact spark that will ignite the mixture and thus start the engine. Thus if the engine should stop in some odd position, and the spark is produced when the piston is slightly before top center, for instance, there will be a slight reverse impulse which will bring another cylinder on the power stroke and into the ignition circuit. The engine will thereupon take up its cycle in the proper direction. In the Bosch duplex system the coil is in series with the magneto armature, but the spark is produced under the same condition, that is, on the breaking of the circuit. In consequence the Bosch duplex system will permit the production of a spark during the first three-quarters of the power stroke by the pressing of the push button set on the switch plate. [Illustration: The Herz High Tension Magneto in Which the Magnets are Built up of Thin Steel Plates Without Pole Pieces (Four Cylinder Type). ] The Bosch two independent system is composed of a separate Bosch battery system and a separate Bosch magneto. Although the operation of the coil is somewhat similar to that of the dual system, the nature of the battery system is such as to require arrangements for two separate sets of spark plugs. The coil is not unlike that supplied with the dual system in that by pressing a button located on the switch plate a series of intense sparks may be produced in the cylinder at all advantageous points of the power stroke. CHAPTER IX CARBURETORS (105) Principles of Carburetion.