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Rh arm towards pushing the sleeve outwards. Now, the end of this lever is attached by means of a short coil spring, and a chain, to a foot or hand applied lever in the body of the car, by operating which the driver can increase or reduce the pressure on, and can consequently regulate the speed of the engine to any degree within the maximum and minimum limits, and so alter the speed of the car without changing the gears. For example, when travelling on a level road at top speed, if the driver wishes to slow down to pass a vehicle, he does not necessarily change his gear, but operates the accelerator, so as to alter the speed of the engine. The car will then slow until the pressure on sleeve is once more increased by means of the lever. Of course, in climbing steep hills, the engine, as a rule, will require its maximum power, and the accelerator must be operated to bring the greatest pressure possible on.

(6) Governing by Throttle.—This system has come into considerable vogue recently, and is now used on Panhard, Napier, Daimler, and other cars. It consists in controlling the speed of the engine by regulating the quantity of mixture admitted to the combustion chamber. This is not done by means of a hand lever, as described in (1) and (2), but is automatically worked by a governor, similar to that described in fig. 17, but simpler. The system being the same, it is hardly necessary to describe it at length.

The action of the governor arms operates a lever which in turn works a throttle valve situated in the supply pipe, close to the carburetter. This valve takes the form of a hollow plunger in which there are perforations, corresponding to similar apertures in the plunger slide. When the engine is working at its fullest power at maximum speed these apertures correspond, and consequently the largest amount of mixture passes to the combustion chamber. When, however, the work lightens and the engine begins to race, the governor comes into operation, and the holes in the plunger and plunger slide eclipse each