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.

The essential elements of any electrical ignition system, either high or low tension, are: First, a simple and practical method of current production; second, suitable timing apparatus, to cause the spark to occur at the right point in the cycle of engine action; third, suitable wiring and other apparatus to convey the current produced by the generator to the sparking member in the cylinder. The important part the storage battery plays in the gasoline automobile can be readily understood by the reader.

Storage Battery for Starting Automobile Motors.-One of the most recent applications of the storage battery is in starting gasoline engines used in automobiles. The storage battery has made the old hand crank obsolete, and has provided a convenient lighting system as well as a positive motor-starting means. The parts of a two-unit starting and lighting system are shown at Fig. 56. This system is sometimes called a "three-unit" system, on account of having a source of independent current supply for ignition purposes. As will be observed, the generator is driven from the motor crankshaft by silent chain connections, one of the terminals. passing through the cut-out device and to the storage battery, the other terminal running directly to the storage-battery terminal, having a short by-pass or shunt wire attached to the cut-out. All the time that the engine is running the generator is delivering electricity to the storage battery.

It will be observed that the storage battery is also coupled to the lighting circuits, which are shown in a group at the right of the illustration, and to the electric-starting motor as indicated. One of the storage battery terminals is joined directly to the switch

terminal by a suitable conductor, the other goes to one of the terminals on the starting motor, while the remaining terminal of the starting motor goes to the switch. In this system, when the small sliding pinion is meshed with the flywheel gear, the switch is thrown on simultaneously, and the current that flows from the storage battery through the windings of the starting motor rotates the engine crankshaft by means of reduction gears shown. As soon as the engine starts the foot is released and a spring pulls

Lighting System.

the switch out of contact, and also disengages the sliding pinion. from the flywheel gear. Electrical starting systems are usually operated on either six- or twelve-volt current, the former being generally favored because the six-volt lamps use heavier filaments than those of high voltage, and are not so likely to break, due to vibration. It is also easier to install a six-volt battery, as this is the standard voltage that has been used for many years for ignition and electric lighting purposes before the starting-motors were applied.

In referring to a system as a one-unit system of lighting, starting and ignition, one means that all of these functions are incorporated in one device, as in the Delco system at Fig. 55. If one

unit is used for generating the lighting and starting current, and also is reversible to act as a motor, but a separate ignition means is provided, such as a high-tension magneto, the system is called a "two-unit" system. The same designation applies to a system when the current generating and ignition functions are performed by one appliance, and where a separate starting-motor is used. The three-unit system is that in which a magneto is employed for ignition, a generator for supplying the lighting and starting current, and a motor for turning over the engine crankshaft.

The generator, as is apparent from its name, is utilized for producing current. This is usually a miniature dynamo patterned largely after those that have received wide application for generating current for electric lighting of our homes and factories. The generators of the different systems vary in construction. Some have a permanent magnetic field, while others have an excited field. In the former case permanent horseshoe magnets are used, as in a magneto. In the other construction the field magnets, as well as the armature, are wound with coils of wire. In all cases the dynamo or generator should be mechanically driven from the engine crankshaft, either by means of a direct drive, by silent chain, or through the medium of the timing or magneto-operating gears. Belts are apt to slip and are not reliable.

All the current produced by the generator and not utilized by the various current-consuming units, such as the lamps, ignition system, electric horn, etc., is accumulated or stored in the storage battery, and kept in reserve for starting or lighting when the engine is not running or for lighting and ignition when the car is being run at such low speed that the generator is not supplying current. Storage batteries used in starting systems must be of special design in order to stand the high discharge and to perform efficiently under the severe vibration and operating conditions incidental to automobile service. The storage battery may be installed on the running-board of the automobile, under the body, or under the front or rear seat, the location depending upon the design of the car and the degree of accessibility desired, as shown at Fig. 57. The best practice is to set the storage battery in a substantial carrying case held by rigid braces attached to the frame

side and cross members. If the battery should be set under the tonneau floor boards, a door must be provided in these to give ready access to the battery.

The starting-motor, which takes the place of the common handcrank, is operated by current from the storage battery, and the

high-speed armature rotation is reduced to the proper cranking speed by reduction gears of the different forms, to be described in proper sequence. The construction of the starting-motor is practically the same as that of the dynamo, and it operates on the same principle, except that one instrument is a reversal of the other.

In order to secure automatic operation of a lighting and start

ing system several mechanical and electrical controls are needed, these including the circuit breaker, the governor, which may be either mechanical or electrical, and the operating switches. The circuit breaker is a device to retain current in the storage battery under such conditions that the battery current is stronger than that delivered from the generator. If no circuit breaker was provided the storage battery could discharge back through the generator winding. The circuit breaker is sometimes called a "cutout." The circuit breaker is usually operated by an electro-magnet, and may be located either on the generator itself or any other convenient place on the car, though in many cases the circuit breakers are usually mounted on the back of the dashboard. This device is absolutely automatic in action and requires but little attention.

The governors are intended to prevent an excessive output of current from the generator when the engine runs at extremely high speed. Two types are used: one mechanical, operated by centrifugal force, and the other electrical. The former is usually a friction-drive mechanism mounted on the generator shaft, which automatically limits the speed of the dynamo armature to a defi- . nite predetermined number of revolutions per minute. The maximum current cutput is thus held to the required amount independently of the speed at which the car is being driven. The use of this device minimizes the possibility of overheating the generator overcharging the battery at high car speeds. The electrical system of governing does not affect the speed of the armature, but controls the output of the generator by means of armature reaction and a reversed series field winding. The governors usually permit a maximum generator output of from ten to twelve amperes, though the normal charging current is less than this figure.

In practically all systems an amperemeter is mounted on the dash so that it can be readily inspected by the driver, this indicating at all times the amount of current being produced by the dynamo or drawn from the battery. If the indicating needle of the amperemeter points to the left of the zero point on the scale, it means that the battery is furnishing current to the lights or other current-consuming units or discharging. When the needle points to the other side of the scale, it means that the generator