To keep a practically continuous forward movement on the driving-shaft, many motors are made with four cylinders, the piston of each being connected with the crank-shaft at a different angle, and each cylinder doing a different part of the work; for example, while No. 1 cylinder is doing the work from the force of the explosion, No. 2 is compressing, No. 3 is getting a fresh supply of gas, and No. 4 is cleaning out waste gas. A four-cylinder motor is practically putting forth power continuously, since one of the four pistons is always at work. While this takes long to describe, the motion is faster than the eye can follow, and the "phut, phut" noise of the exhaust sounds like the tattoo of a drum. Almost every gasoline motor vehicle carries its own electric plant, either a set of batteries or more commonly a little magneto dynamo, which is run by the shaft of the motor. Electricity is used to make the spark that explodes the gas at just the right moment in the cylinders. All this is automatic, though sometimes the driver has to resort to the persuasive qualities of a monkey-wrench and an oil-can. The exploding gas creates great heat, and unless something is done to cool the cylinders they get so hot that the gas is ignited by the heat of the metal. Some motors are cooled by a stream of water which, flowing round the cylinders and through coils of pipe, is blown upon by the breeze made by the movement of the vehicle. Others are kept cool by a revolving fan geared to the driving-shaft, which blows on the cylinders; while still others--small motors used on motor bicycles, generally--have wide ridges or projections on the outside of the cylinders to catch the wind as the machine rushes along. The inventors of the gasoline motor vehicles had many difficulties to overcome that did not trouble those who had to deal with steam. For instance, the gasoline motor cannot be started as easily as a steam-engine. It is necessary to make the driving-shaft revolve a few times by hand in order to start the cylinders working in their proper order. Therefore, the motor of a gasoline machine goes all the time, even when the vehicle is at rest. Friction clutches are used by which the driving-shaft and the axles can be connected or disconnected at the will of the driver, so that the vehicle can stand while the motor is running; friction clutches are used also to throw in gears of different sizes to increase or decrease the speed of the vehicle, as well as to drive backward. [Illustration: AN AUTOMOBILE BUCKBOARD]