Page:Motors and motor-driving (1902).djvu/188

156 into contact. If the distance between the contacts is correctly judged, the trembler will vibrate freely, thereby causing several 'makes and breaks' in the circuit. As previously explained, a stream of sparks will result in the combustion chamber.

And, as also explained, it is necessary to alter the moment of firing the charge. To effect this the plate is designed to be easily moved backwards or forwards in relation to the cam. The effect of this is to bring the point of the trembler a little higher up or lower down, causing it to enter the notch earlier or later, so that the moment of contact and consequently the spark is varied according to the will of the operator. The faster the engine runs, the earlier must be the spark.

.—Adjustment of Trembler.—On the correct adjustment of the trembler and the screw much of the success of the De Dion system depends. The means of adjustment is as follows: Unscrew the sparking plug, and attaching the 'secondary' wire, lay the metal portion of the plug on the top of the engine, care being taken that the terminal is well away from any metal. Now smartly turn the motor starting-handle, when a stream of sparks should be observed to cross between the points of the plug. When the trembler is over the notch in the cam, it should have so far entered it as to be resting on when it is half in. If the bottom of the trembler be lifted with the finger and allowed to quickly drop there should be a regular hum or buzz. After a little practice the novice will be able to recognise the correct position for the screw by the hum of the trembler. It should be remembered that, though a stream of sparks may pass between the points of the sparking plug when it is removed from the engine, it does not follow that the same effect will be produced under the conditions of highly compressed gas found in the cylinder.