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

Fig. 349.-Showing Construction of Atwater-Kent Uni-Sparker.

cylinders in such order as to insure proper sequence of explosions. 'The external view of the Atwater-Kent uni-sparker is shown at Fig. 349, A. In this a centrifugal mechanism is contained in the lower part of the 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 B. 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: the screw. The contact point 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 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.

Q. What is the "closed circuit" system?

A. An example of the closed circuit system is shown at C, Fig. 350, and is of Connecticut design, the complete ignition system consisting of a combined timer and high tension distributor, a separate induction coil and a switch. The system is distinctive in that the timer is so constructed that the primary circuit of the coil is permitted to become thoroughly saturated with electricity

before the points separate, with a result that a spark of maximum intensity is produced. The action is very much the same as that of a magneto on account of the saturation of the winding. Another feature is the incorporation with the switch of a thermostatically operated electro-magnetic device which automatically breaks the connection between the battery and coil should the switch be left on with the motor idle.

The contact breaker mechanism consists of an arm ▲ carrying one contact, a stationary block B carrying the other contact, a fiber roller R which is carried by the arm A and operated by points on the cam C, which is mounted on the driving shaft. Normally the contacts are held together under the action of a light spring. As the four cams, which in touching the roller R raise the arm and separate the contacts, are 90 degrees for a fourcylinder motor, the period of saturation of the coil or the length of time the current flows through it to the battery is sufficiently long so that when the points have separated the current which has "piled" up induces an intensely hot spark at the plugs. This is an advantage inasmuch as it insures prompt starting and regular ignition at low engine speed as well as providing positive ignition at high engine speed.

The thermostatic circuit breaking mechanism is very simple. This consists of the thermostat T, which heats when the current passes through it for from thirty seconds to four minutes without interruption, and thus is bent downward, making contact with the contact L. This completes an electrical circuit which energizes the magnets M, causing the arm K to operate like the clapper in an electric bell. This arm strikes against the plate, which releases whichever of the two buttons in the switch may be depressed.

As will be observed, the transformer coil provided has five terminals. One of these is directly connected with the ground, the other leads to the central secondary distributing brush of the timerdistributor. Of the three primary leads, one goes to the switch, one to the wire leading from the storage battery to the timer, and one directly to a terminal on the timer. The switch is provided with three buttons, the one marked B being depressed to start the engine, as the ignition current is then drawn from the storage bat

tery. After the engine has been started the button marked M is pressed in, this taking the current directly from the generator. To interrupt ignition the button "off" is pressed in, this releasing whichever of the buttons, B or M, is depressed. Four wires run from the distributor section of the igniter to the spark plug.

Q. Describe Remy ignition system.

A. The Remy system also operates on the closed circuit principle and is shown at A, Fig. 350, in a form adapted for six-cylinder engine ignition. The transformer coil is of the three terminal type, one secondary going to the central secondary distributing brush of the timer while one primary is joined to the primary contact terminal of the timer portion of the igniter. The remaining coil terminal is joined to the switch. One of the poles of the storage battery and one of the series connected dry cell batteries are grounded, while from the other two the wires run to the switch contacts. The current may thus be derived either from the dry cell batteries for emergency or from the storage battery for regular ignition purposes. The construction of the timer which incorporates the breaker mechanism is clearly shown. The movable platinum contact point is carried by the arm A, which fulcrums on the bearing S, and which has a piece of hard steel F riveted to it to act as a cam rider. The cam C is of hexagonal form, having six points which separate the contacts when they ride over the shoe F attached to the arm A. The fixed platinum contact point B is so arranged that it may be adjusted by moving in or out as conditions demand. It is to the member that the primary terminal of the coil is connected.

Q. Describe typical timer distributor.

A. A typical combined timer distributor known as the Halladay is shown at B, Fig. 350. The make and break mechanism is very simple in design, as is the distributing mechanism. The contact between the platinum points is established by a four point cam. The secondary current is distributed from the central terminal to the four distributing terminals by a carbon brush very much similar in design to that employed in a high tension magneto. This operates on the open circuit principle.