wiring diagram Fig. 34. The advantage of a timer of the form shown, as contrasted to the simple type previously considered, is that a one unit induction coil will serve any number of cylinders from 2 to 8, whereas with the roller type shown at Fig. 31 a separate induction coil is needed for each cylinder to be fired.

Contact Timer.

It will be observed that the coil used with the Atwater-Kent system has five terminals, four of these being primary terminals, one at the center of the coil box a secondary or high tension terminal. A set of six dry cells connected in series is wired to one side of the coil box as indicated. One of the two remaining primary terminals runs to the primary contact at the bottom of the

interrupter, the other to a grounding screw attached to the interrupter casing. The secondary terminal is connected to the central terminal of the distributor, while the remaining four terminals are joined to the plugs in the engine cylinders in such order as to insure proper sequence of explosions. The external view of the Atwater-Kent uni-sparker is shown at Fig. 35, A. In this a centrifugal mechanism is contained in the lower part of the

Fig. 34-Wiring Diagram of Atwater-Kent Uni-Sparker.

casing by which the spark is automatically advanced as the speed of the engine increases.

The only points that will wear on a device of this character are the contact points which are clearly shown in the view of the contact breaker mechanism at Fig. 36. The revolving shaft in the center has a number of notches, two, three, four, six, or eight, according to the number of cylinders to be fired, cut into it. A light, hardened steel trigger, B, is held against the shaft at this point by a small spring. On turning the shaft this trigger is carried forward by the notches in the shaft, and is suddenly released as the hook end leaves the notch. In so doing the back of the trigger

strikes a small pivoted hammer, D, situated between the trigger and the spring carrying the contact points. This causes the contact points, K, to open and close with remarkable rapidity, but one contact being made for each spark. When it is desired to adjust the platinum contact points, as when they show signs of wear, it is only necessary to remove one or more of a number of extremely thin washers under the head of the adjustment screw and to replace

Fig. 35.-Showing Construction of Atwater-Kent Uni-Sparker.

the screw. The contact points should be absolutely clean and bright and have smooth contacting surfaces. The distributor portion of the device consists of a hard rubber block fitted to the top of the primary shaft, this carrying a brass quadrant that passes the high tension current to the spark plugs by means of the terminal points imbedded in the hemispherical cover. There is no actual contact between the rotating quadrant and the distributor points, as the high tension current is capable of jumping the very

Fig. 36.-Diagrams Explaining Action of Atwater-Kent Contact Breaker.

slight gap that exists between them. Owing to there being no actual contact, there will be no depreciation in the distributor or upper portion. The center terminal, which is in connection with the induction coil, is a combination of carbon and brass, and a

light, flat spring on the quadrant bears against it to maintain positive electrical connection. The distributor cover is easily removed without the use of tools, as it is held by spring clips. Location or dowel pins in its lower edge insure that it will be replaced in the correct position.

One of the most popular of the combined starting, lighting and ignition systems is the Delco, which is shown at Fig. 37. For the present we will concern ourselves merely with discussing the ignition functions of the system, leaving the self-starting and electric lighting features for more comprehensive consideration later. Current is produced by a one unit type motor-generator, although the windings of the device when operated as a motor or a generator are entirely separate. The ignition current is obtained either from a storage battery which is kept in a state of charge by the generator, or from a set of dry cells which are carried for reserve ignition. The ignition system consists of a one unit nonvibrator coil, sometimes attached to the top of the motor generator, though it may be placed at any convenient part of the car and a dual automatic distributor and timer usually included as a part of the device as shown. When ignition current is supplied from the lighting circuit the current passes from the storage battery through a switch and out to the low tension winding of the coil, from whence it passes to the timer and from there to the frame, where it is grounded. The high tension current generated in the coil runs to the distributor, where it is switched to the spark plug in the different cylinders in turn.

When dry cells are used for ignition the operation is the same except that a device called "the ignition relay," and shown at the right of Fig. 38, is added to the circuit. The function of this device is to break the circuit immediately after it has been completed by the contact points of the timer, which is shown at the left. The use of the ignition relay results in a material saving of the battery current as the circuit is closed a much shorter time than is the case when the circuit is broken by the timer contacts themselves. The operation of the relay is not difficult to understand. The magnet A attracts the armature B when the circuit is completed through the timer. This action opens contact C and