=Magnetic Vibrators.=--Many types of vibrator are used on induction coils, the most important requirement being that _the break occur with great rapidity_. In order to render the break as sudden as possible, different expedients have been resorted to, all tending to make the mechanism more complicated, yet having sufficient merit in some cases to warrant their adoption. In the plain vibrator, the circuit is broken at the instant the spring begins to move, hence, the operation must be comparatively slow. In order to render the break more abrupt some vibrators have two moving parts, one of which is attracted by the magnetic core of the coil and moved a certain distance before the break is effected. A vibrator of this type is shown in fig. 146 and described under the illustration. [Illustration: FIG. 146.--A hammer vibrator. When at rest, the upward tension of the spring, which carries the armature A, holds the platinum points in contact and causes the upper spring C, to leave shoulder of adjusting screw D, and rest against the heavy brass plate above it. When the iron core B, attracts the armature A, the downward tension on the upper spring, C, causes the latter to follow the armature down, holding the platinum point in contact, until the end of the upper spring C, strikes the lower shoulder of the adjusting screw, D, which gives it a “hammer break.” The adjusting screw is held firmly in position by a bronze spiral spring under shoulder D.] =Vibrator Adjustment.=--When a vibrator coil is used, the quality of the spark depends largely upon the proper adjustment of the vibrator. The following general instructions for adjusting a plain vibrator should be carefully noted: 1. Remove entirely the contact adjusting screw. 2. See that the surfaces of the contact points are flat, clean and bright. 3. Adjust the vibrator spring so that the hammer or piece of iron on the end of the vibrator spring stands normally about one-sixteenth of an inch from the end of the coil. 4. Adjust the contact screw until it just touches the platinum contact on the vibrator spring--be sure that it touches, but very lightly. Now start the engine; if it miss at all, tighten up, or screw in the contact screw a trifle further--just a trifle at a time, until the engine will run without missing explosions. TABLE OF INDUCTION COIL DIMENSIONS.