When this occurs the first thing is to examine the conductors and ascertain whether the insulation is intact. Sometimes the insulation becomes worn or frayed, and it is not infrequent for the ends of the wire, where attached to the binding post to spread out, where the conductor is made up of a lot of small wires, and some of them touch the metal alongside of the binding post. SHORT CIRCUITING OF SECONDARY WIRES.--The secondary wires often cause short circuiting by lying too close to the metal of the engine or case. Great care should be observed to use the best insulated wire, and to see that they are free from dangerous contact. Stranded cables are better for all wiring purposes, as vibration will not affect the screws which hold them at the contacts. A solid wire will cause a constant jar, and affect all connections. CHAPTER XIII AUTOMOBILE ACCESSORIES Self-starting devices are the latest permanent addition to a perfect car equipment. Two general types are being made, one purely mechanical in its character, and the other operated by the engine itself. The mechanical devices usually have some connection with the forwardly-projecting end of the crank shaft, where the present cranking shaft is located, and some of the inventions in this respect have an arrangement whereby the driver is able manually to operate the starter from his seat. The actual work of turning the shaft is now performed by compressed air which actuates mechanism that gives from one to two turns to the shaft, sufficient to ignite the fuel in several of the cylinders. SIMPLE TYPE OF STARTER.--The simplest type of starter is that which utilizes the cylinders themselves to give the initial turns. To illustrate the matter we have given some sketches of the engine cycle, in Fig. 95. The four positions of the piston in a four-cylinder engine are so placed that the spark cannot ignite the charge in either cylinder. Cylinders 1 and 2 are descending, and 3 and 4 are ascending. The charge in 4 is partially compressed, but it must reach the position indicated by the dotted lines A before it can be ignited. [Illustration: Fig. 95. Starting Mechanism.] The sparking mechanism was cut off before the cylinder 1 reached its highest point, at the previous stopping of the car, so that it still has an unexploded charge; and piston 3 is now discharging the gas from that cylinder. As the engine is now at rest, the problem is to supply a charge to cylinder 1, or a pressure of sufficient strength to turn the engine shaft so that the piston in 1 will be brought up to the explosion line A. It is accomplished in the following manner: One or more of the engine cylinders is connected up by a small pipe with a storage tank, located at any convenient point, so that at each explosion a portion of the charge in the cylinders goes into the tank, where it is held by a check valve.