Current from the battery R passes through the coil winding P to the coil terminal U from which it passes from V to the igniter binding post J. From J it flows along the rod D to the stationary electrode A. Since the rod D is surrounded by the insulating washers and tube H, T and I, the current cannot escape directly to the casing K. With the two platinum points N and O in contact, the current flows through C to the shell K from which point it flows back to the battery R through the conducting path V, completing the circuit. The greater portion of the path V consists of the engine frame. When the electrode is moved in the direction of arrow B, the current is opened and a spark occurs at the point of separation M, in contact with the gas in the combustion chamber. The electrode C being connected with the engine frame is said to be “grounded.” If the stationary electrode A were not insulated from the casting K, the current would pass directly from the terminal J back to the battery R without passing through the contact points at all, and consequently no spark would be produced on the separation of the points. [Illustration: Fig. 93. Diagram of Igniter and Connections. ] A push rod which is actuated by a cam on the engine, engages with the trigger G, and causes the spark to occur when the piston is on the end of the compression stroke. In nearly all engines, the relation between the time of the spark and the piston position can be regulated to suit the requirements for advance and retard. This adjustment is necessary in order that the spark may be varied to meet the difference between the starting and running requirements. While the ignition should be considerably advanced while running, it is necessary to retard it when starting, as the engine is liable to “kick back” with an advanced spark. This advance and retard device should be accessible while the engine is running, and the operator should be able to control the point of ignition at all times. Many men have been seriously injured by the lack of this device or by neglecting to use it. The contact points make contact only for a short time before the spark is required in order to reduce the amount of current to the minimum, and therefore increase the life of the batteries. The duration of the “make” or contact should be as short as possible. Prolonged contact weakens the batteries and causes them to run down rapidly. For the same reason the electrodes should remain separated until the make is actually required. A certain period of contact is necessary, however, to allow the spark coil to “build up,” but with a properly designed coil the time required is very short. Some engines provide a device that cuts out the ignition current altogether during the idle strokes. This adds materially to the life of the batteries.