FEED.--The method of conveying the petrol from the main tank to the carburettor. If the tank is higher than the carburettor, the petrol will pass by gravity. Otherwise it must be lifted by pressure. The exhaust is generally employed for this purpose, a hand-pump being fitted to furnish the necessary pressure for starting. FLY-WHEEL.--As only one of the four strokes of the motor is a working stroke, a heavy fly-wheel is necessary to carry the piston through its cycle and promote easy running. FRAME.--The structure which carries the machinery of the car. GARAGE.--A stable for motor-cars. GEARS.--_See_ Bevel Gear, Change-speed Gear, Differential Gear. GOVERNOR.--The appliance which automatically regulates the speed of the engine, usually by checking the volume of mixture admitted to the cylinder. GRADIENT.--The inclination or slope of a road. GRAVITY FEED.--_See_ Feed. HORSE-POWER.--Boulton and Watt calculated that a London dray-horse was capable of work equivalent to lifting 33,000 lb. one foot high in one minute, and this task--technically described as 33,000 foot-lb. per minute--has been accepted as the “unit of horse-power” for the measurement of mechanical work. The power of a petrol motor depends upon many factors--diameter of cylinder, speed of working, quality of mixture, compression, cooling-surfaces, &c.--some of which vary from moment to moment in practice. The only real means of measuring it is by the dynamometer or pony-brake, which records the power actually available for useful work. Horse-power so measured is called brake horse-power. For purposes of competitions the Royal Automobile Club use the following formula for rating the comparative power of petrol motors. Multiply the diameter of the cylinder in inches by itself and again by the number of cylinders. The product divided by 2¼ is the nominal horse-power. IGNITION.--_See_ Electric Ignition. INDUCTION-COIL.--An apparatus for intensifying the pressure of the electric current. Used in motor practice as a part of the system of high-tension ignition. INSPECTION PIT.--A pit or well, generally situated in or near the garage, to facilitate the examination and repair of the chassis of a car. LICENCES.--Licences must be taken out (1) by the owner of a car. This licence costs from two to five guineas according to the weight of the car; and (2) the driver of a car. This costs five shillings only. LIMOUSINE.--A large covered car. LIVE AXLE.--_See_ Axles. LUBRICATION.--The application of oil, grease or other substances suitable for the reduction of friction between sliding surfaces. MIXTURE.--The explosive charge of petrol and air admitted to the cylinder. _See_ Carburettor.