*Carbon.* A material like coke, ground or crushed, and formed into sticks or plates by molding or compression. It requires a high heat to melt or burn, and is used as electrodes for arc lamps and for battery elements. *Carbonization.* Coated with carbon. Turned into the form of carbon. *Cell.* A vessel containing an electrolyte and two elements. *Centrifugal.* The outwardly-moving force from a rotating body. *Change-speed gears.* The part of an automobile which is in the line of the driving shafts, and designed to change the speed of the axle relative to the speed of the engine shaft. *Channel bars.* A bar made U-shaped in cross section. *Chemical action.* A term to describe the change brought about by uniting chemicals of different kinds. *Circuiting.* The manner of wiring up an electric device so the current will perform its work. *Circumferential.* Around the outside, *Clearance.* That space in the head of an engine cylinder, above the piston, in which the gas is compressed previous to igniting it. *Clutch.* A mechanism which is placed on the abutting ends of a pair of shafts, and designed to couple or uncouple the two shafts together. *Cooperation.* Acting in unison. In harmony. *Combustion chamber.* That part of a cylinder in which the gases are ignited and expanded. *Comminuted.* Finely divided. A powder. *Commutator.* A cylinder on the end of the armature of a dynamo or motor, and provided with a pair of contact plates for each particular coil in the armature, in order to change the direction of the current. *Compression.* A term used to designate the forcing together of the carbureted air drawn into the chamber of an internal combustion engine. *Compensate.* Paying for a thing; to give ample in return.