682,460. Ignition systems. GENERAL MOTORS CORPORATION, Feb. 15, 1950 [Feb. 16, 1949], No. 3824/50. Class 7 (iv). In an ignition system comprising a main condenser 44 connected to the primary 45 of an ignition coil 46, to the secondary 47 of which the spark plug 48 is connected, means, such as a voltage doubler having series connected condensers 36, 37, fed from a cold cathode rectifier 31, for charging the main condenser, a thyratron 43 controlling the discharge thereof, an auxiliary condenser 59 connected to the charging means, and through contact breaker contacts 55, 56 to the grid 43a of the thyratron 43, there is provided a spark prolonging condenser 61, also connected to the . charging means and to the spark plug 48 through the secondary 47 of the ignition coil 46, which discharges to maintain the arc for a longer period! than would otherwise result from the discharge of the main condenser 44 alone through the ignition coil primary 45. The ignition system is energized from either a battery 10 or a generator G connected through an ignition switch 17 and a suppressor with the centre taps of a two-part primary winding of a transformer 11, which primary is associated with a vibrator 21 having two separate sets of contacts 26, 28 and 27, 29 each set being in circuit with one part only of the primary winding in order to reduce the current carried by the contacts. The transformer secondary winding 16, which is shunted by a condenser 34 that absorbs any transients caused by the vibrator operation, is connected, through the voltage doubler to a terminal 39 maintained at a potential of between 800-1,500 volts depending upon the state of charge of the battery. Terminal 39 is connected to the spark prolonging condenser 61, the anode of the thyratron 43, a resistance 42 and the main condenser 44; the other end of resistance 42 is joined to a wire 50 between which and another wire 53 is a voltage regulator 52 that limits the voltage across these wires to, say, 750 volts, and the auxiliary condenser 59, one plate of which is earthed and connected to the cathode of the cold cathode thyratron 43. The voltage regulator 52 ensures adequate charging of condenser 59 irrespective of the potential of terminal 39 since it will not pass current if the applied voltage is less than 750 volts, whilst any voltage in excess of 750 is absorbed in resistance 42. When the engine operated contacts 55, 56 are closed condenser 59 discharges to grid 43a and thyratron 43 becomes conductive so that main condenser 44 discharges through primary 45 and causes break-down of the sparking plug 48 whereby the circuit for discharge of condenser 61 is completed, which discharge prolongs the spark across the plug gap. The rate of discharge of condenser 44 is greater than its rate of charge from terminal 39 so that upon cessation of its discharge the thyratron will again become non-conductive. The invention is particularly useful to enable sufficient heat to be given to the combustible mixture when using plugs with short spark gaps. Specification 626,190 is referred to.