the vibrator blade is connected with one of the ends of the primary coil. The other end of the primary coil goes to the terminal which is joined to the ground. The condenser is shunted in between the vibrator points, i. e., one of the leads is attached to terminal No. 1 while the other is soldered to the end of the primary coil which goes on the vibrator spring member. One end of the secondary coil is attached to terminal No. 2, which is grounded on some metal

Fig. 26.-Part Sectional View of Simple Induction Coil, an Important Component of All Battery Ignition Groups and Sometimes Used with Magnetos.

part of the chassis frame, while the other end is secured to terminal No. 3, which is joined to the spark plug electrode. After the various components of the induction coil are assembled in the box and the connections made as indicated, the spaces between the sides of the box and the coil member are filled with an insulating compound composed of bees-wax, pitch and rosin. This holds everything rigidly in place and prevents the wire joints loosening through vibration. The external appearance of a one-cylinder box coil of the vibrator type is shown at Fig. 27.

The method of connecting the members of an induction coil,

shown at Fig. 26, is a conventional one, though the connections will differ with the nature of the circuit of which the coil forms a part and the number of units comprising the coil assembly. When such devices are employed for igniting multiple-cylinder motors, the internal wiring is very much the same as though the same number of

box coils for single-cylinder ignition were com

ADJUSTMENT bined together by out

VIBRATOR

SECONDARY
TERMINAL

side conductors. The number of terminals provided will vary with the number of units. Various forms of induction coils are depicted at Fig. 28. That at A is a simple unit form in which the coil is attached directly to the spark plug, which in turn is screwed into the cylinder. On this coil but two primary terminals are attached, one being connected to the insulated contact point on the timer, the other being grounded, or attached to the battery.

Fig. 27.-Three Terminal Box Coil for Single
Cylinder Engine Ignition.

Coils of this type have been very popular in marine application because of the simple and direct wiring possible, but they have not been used in connection with automobile engine ignition to any extent. The form shown at B is a simple dash coil for onecylinder use which has three terminals, one being used for a secondary lead to the spark plug, the other two being joined to the battery and ground respectively, as shown at Fig. 26.

The form of coil shown at C is a two-unit member designed for double-cylinder ignition. As the switch is mounted on the coil box

to use two sets of batteries, six terminals are provided on the bottom of the coil case. Two of these are attached directly to the insulated contact point of the timer; two others which are enclosed in hard rubber insulating caps are attached to the spark plugs. The two immediately under the switch are attached to the free terminals of the battery, two sets being provided, one being coupled to each side of the switch.

With a four-unit coil, as shown at D, ten terminals are provided because of the attached switch. Four go to the spark plugs, four to the insulated segments of the timer and two to the battery, or battery and magneto or dynamo, as the case may be. In modern coils the units may be removed from the box without disturbing any internal connection, and a new one slipped in its place if it does not function properly. Special care is taken in insulating the hightension terminal by means of rubber caps which surround the wire, and care is taken to have the vibrator contact points readily accessible for inspection, cleaning, or adjustment.

Action of High Tension Coil Ignition System.-Another explanation of the action of the conventional induction coil and battery system may enable the reader to obtain a clearer understanding of the action of the transformer coil system of intensifying current and can be read to advantage to supplement the explanation previously given. Another diagram, Fig. 29, shows a four terminal coil unit instead of the three terminal coil diagram outlined at Fig. 25, and differs in that the primary and secondary circuits have separate ground connections instead of having a common terminal on the coil. As the internal construction of the induction coil has been previously described, it will be merely necessary to review the action of the complete ignition system outlined.

In the diagram shown the action is as follows: When the switch E is closed and the rotor (f) of the spark-timing device D comes in contact with the terminal (g), the current flows from the positive terminal (m) of the battery to the switch E. From thence to the primary terminal (h) on the coil; and through the vibrator spring (e) across the points (o) which are in contact, to the adjusting screw (i) and into the bridge which supports the adjusting screw. The primary winding (b) is attached to this bridge at (j) and

the current flows through it to the terminal (k), from which terminal it is carried to the point (g) on the commutator and into the rotor (f). A metal brush takes up the current at this point and it is carried to the negative terminal (n) of the battery, passing through the battery it reaches the point (m) from which it started. The current will not flow unless the circuit is complete,

and it cannot be complete unless the rotor (f) touches the terminal (g). This rotor is so set on the engine and so timed in relation to the movement of the piston that it will complete the circuit only at the time the spark is desired in the cylinder. When the current flows through the primary winding it makes a magnet of the core and enables it to attract the armature, as a magnet will attract pieces of iron or steel, and the armature is made of magnetic material.