CAM, a portion of a machine used for converting rotary mo tion into reciprocating or intermittent motion, or vice versa. It consists of a disk usually mounted on a revolving shaft, the peri phery of the disk having a varying radius so its motion is eccentric. Against this turning surface a rod or other shaped piece, called a "follower," slides or rolls. A simple type of cam would be an egg shaped metal plate with a shaft attached at right angles to its sur face and, lying against the periphery of the plate, a rod. If now the shaft, and therefore the plate, be made to revolve, the rod will rise and fall. For resetting the hand of a stop watch to zero, a small spring-restrained arm carrying a roller on its end presses against a heart shaped cam which revolves nearly around the re-entrant point of the heart. Cams are also used for making and breaking contacts suddenly, such as the double logarithmic spiral cams used for sending out impulses from master clocks. Cams are also used in connection with the valve gear of internal combustion engines.