JUMP-SPARK SYSTEM
The jump-spark or high-tension system of ignition depends on the production of a current at such a pressure that it can jump from one point to another through high resistance, such as is presented by air at ordinary or low temperature, and especially when compressed, the spark occurring as it passes.
This high pressure is obtained through the use of a secondary induction coil, which consists of a core and primary winding similar to those of the primary induction coil already described, and in addition has a secondary winding, formed by a great length of insulated copper wire, which to save bulk and weight is very fine, wound over the primary winding. The change in the strength of the magnetic field produced by the core affects this secondary winding, just as it affects the primary winding; that is, a current is set up in it at every change in the strength of the magnetic field, the pressure of the current depending on the greater or less extent of the change, and the rapidity with which it occurs. The magnetization of the core takes place but slowly, for the particles of iron must absorb it one from the other, but the demagnetization occurs instantly; the current that is induced during the demagnetization is therefore the greater, and is the current that has sufficient pressure to jump across the gap.
The ignition system employing this coil consists of two distinct parts: the primary circuit, which magnetizes the core, and the secondary circuit, which leads to the combustion space the current that is induced in the secondary winding.
The primary circuit includes the battery or generator that supplies the current, the primary winding of the coil, a timer, and a vibrator.