has to serve for the whole cycle; in other words, for two complete revolutions of the crank. A single-cylinder steam-engine develops an impulse every half-turn—that is, four times as often. In order to get a more constant turning effect, motor cars have two, three, four, six, and even eight cylinders. Four-cylinder engines are at present the most popular type for powerful cars.
THE MOTOR CAR.
We will now proceed to an examination of the motor car, which, in addition to mechanical apparatus for the transmission of motion to the driving-wheels, includes all the fundamental adjuncts of the internal-combustion engine.8 Fig. 40 is a bird's-eye view of the chassis (or "works" and wheels) of a car, from which the body has been removed. Starting at the left, we have the handle for setting the engine in motion; the engine (a two-cylinder in this case); the fly-wheel, inside which is the clutch; the gear-box, containing the cogs for altering the speed of revolution of the driving-wheels relatively to that of the engine; the propeller shaft; the silencer, for deadening the noise of the exhaust; and the bevel-gear, for turning the driving-wheels. In the particular type of car here considered you will notice that a "direct," or shaft, drive is used. The shaft has at each end a flexible, or "universal," joint, which allows the shaft to turn freely, even though it may not be in a line with the shaft projecting from the gear-box. It must be remembered that the engine and gear-box are mounted on the frame, between which and the axles are springs, so that when the car bumps up and down, the shaft describes part of a circle, of which the gear-box end is the centre.
An alternative method of driving is by means of