Fig. 39. & Fig. 40
Figs. 39 and 40 are the most generally used burners, the wire from the condenser being attached to the lug or top electrode, which is insulated from the burner by means of the mica plate to which it is riveted. The burner pillars are of course grounded through their being screwed into the gas pipe. The circuit is shown in Fig. 41. I is the induction or Ruhmkorff coil, in the primary circuit of which is the key, K, controlling the current from the battery, B, and across which is bridged the condenser, C C. When the coil vibrator is used, the condenser C C can be omitted, that of the coil itself serving instead. S is the wire leading from the secondary terminal of the coil to the burner condenser, C, which, in turn, are connected to the electrodes on the burners, P P, as before noted. The other secondary wire is grounded preferably to the gas pipe itself.
Fig. 41.
Where a lot of burners are placed together, as in a ring, it is often feasible to light them by contagion, one tip only being connected to the coil circuit, the others lighting from it and conveying the flame around to the rest. This avoids multiplicity of circuits, or, perhaps, too many burner gaps on one circuit; but the one burner may fail to light, whereas, where all are fitted, the chances of failure are less, especially in the Edwards condenser system.
Switch for Jump Spark-lighting.
In a switch for controlling the current of the secondary coil it will be evident that the utmost attention must be paid to matters of insulation. The object of such a switch is to control a number of circuits; for example, as it is not advisable to put more than 20 to 25 burners on one circuit, a case requiring the lighting of 100 burners would necessitate some means of passing the current to each circuit in turn. This is shown in Fig. 42, in which S is a hard rubber plate, provided with a revolving metal arm and handle, H, and four contact points, P, which latter receive the ends of the wires from the groups of burner condensers B by means of nuts or binding posts. The wire from the secondary of the coil is run to the switch-handle, H, great care being taken that it does not pass near to the circuit wires, or contact points. Revolving the switch-handle connects the secondary wire to each circuit in turn. It will be noticed that, unlike a battery switch, this one has a large base, long switch-arm, contact points situated far apart, and every precaution taken to control the passage of the high-tension current. The base should always be of rubber or glass. Shellacked-wood, or such substitutes, are productive of trouble.
Fig. 42.
When it is desired to light automatically a number of burners from a distance, the Trailer (Fig. 43), is used. This is a switch similar to above, but the arm is revolved by means of toothed wheels by the electro-magnet shown on the back. As it is never desirable to unnecessarily prolong the secondary wires, this device admits of the switch being put near the circuits, and yet being operated from afar.