The secondary winding of fine wire is a continuation of the primary winding, and the secondary is wound directly over the primary. The outer end of the secondary connects with the slip ring (9) on which slides the carbon brush (10), which conducts the high tension current from the armature. This brush is insulated from the frame by the insulation (11). From (10) the current is led through the bridge (12) through the carbon brush (13) to the distributor brush (15). Metal segments are imbedded in the distributor (16), the number of which corresponds to the number of cylinders. As the brush rotates, it makes consecutive contact with each of the segments in turn and therefore leads the current to the cylinders in their firing order. Wires from the cylinders are connected to sockets that in turn connect with the segments. The disc driving the distributor brush (15) is geared from the armature shaft in such a way that the armature turns twice for every revolution of the distributor, when four cylinders are fired, and three times for the distributors once when six cylinders are fired. [Illustration: Fig. 108. Bosch High Tension Circuit. ] The voltage of the current generated in the secondary coil by the rotation of the armature is increased by the interruption of the primary circuit caused by the opening of the contact breaker. At the instant of interruption of the primary circuit the high tension spark is produced at the spark plug. As the spark must occur in the cylinder of the engine at a certain position of the piston, it is necessary that the interrupter act at a point corresponding to a definite position of the piston, consequently this type of magneto must be driven positively from the motor by means of gears, or directly from the shaft. These magnetos run in only one direction. This running direction should be given when magneto is ordered, as being “clockwise” or “counter-clockwise” when looking at the driving end of the magneto. The magneto for the single and double cylinder engines has no distributor, the high tension current being led directly from the armature. The circuit diagram of the Bosch four cylinder magneto is shown by Fig. 108, the winding and plug connections being clearly shown. When connecting the magneto care should be taken to have the distributor and plug connections arranged so that the cylinders will fire in the proper order. (101) Bosch Oscillating High Tension Magneto. The oscillating type of magneto is used on slow speed heavy duty engines that move too slowly for the ordinary type of magneto. In the oscillating type the armature is given a short angular swing by the action of a tripping device operated by the engine which results in an intense spark at the lowest speeds. Magneto type “29” is constructed with two powerful steel magnets, while magneto type “30” is provided with three; an armature of the shuttle type is arranged to oscillate between their pole-shoes.