safety spring and mounted on an eccentric spindle, the position of which can be varied by means of a regulating-lever (I). The rod is operated from the distributing-shaft, on the conical end of which a cam J carrying a spindle is secured.

Fig. 19.—Contacts of the Winterthur system.

Regulation of the Magneto.—The position assumed by the armature when at rest is a matter of importance in obtaining a good spark on breaking the circuit. The marks on the armature should be noted. The position

of the armature may be experimentally varied, in order to obtain a spark of maximum intensity, by changing the position of the arm B on the armature-shaft.

Control of the Magneto.—The controlling gear should enable the armature to oscillate from 20 to 25 degrees. The time at which the breaking of the circuit is effected can be regulated by shifting the handle (I). In starting the engine, the circuit can be broken with a slight retardation, which is lessened as the engine attains its normal speed.

Igniter.—It is advisable that there should be a play of ¹⁄₂ mm. (0.0196 in.) between the lever Z when at rest and the striking-pin. The axis D of the circuit-breaking device should be easily movable; and the hammer which it carries at its end toward the interior of the cylinder should be in perfect contact with the stationary spindle M, which is electrically insulated. This spindle M should be well enclosed, in order to prevent any leakage that might cause a deterioration of the insulating material.

The subject of ignition is of such extreme importance that the author will recur to it from time to time in the various chapters of this book. Too much stress cannot be laid upon proper timing; otherwise there will be a needless waste of power. Cleanliness is a point that must be observed scrupulously; for spark-plugs are apt to foul only too readily, with the result that short-circuits and misfires are apt to occur. In oil and volatile hydrocarbon engines the tendency to fouling is particularly noticeable. In the chapter devoted

to these forms of motors the author has dwelt upon the precautions that should be taken to forestall a possible derangement of the ignition apparatus. As a general rule the ignition apparatus installed by trustworthy manufacturers will be found best suited for the requirements of the engine.

The apparatus should be fitted with a device by which the ignition can be duly timed by hand during operation (Fig. 17).