INDICATOR

an instrument for recording diagrammatically on a card the behavior of steam in the cylinder of an engine. The piston is connected with a lever, the end of which carries a pencil (usually a bra point) for making the diagram. The actual movement of the piston is magnified in the diagram. The indicator card (of metal) is wrapped round a drum, which is made to oscillate on its axis, being connected with the cro head of the engine by a cord pa ing round a groove at its base. Various springs serve to adjust the indicator cylinder to varying conditions. The expansion and compre ion curves thus obtained are in the form of rectangular hyperbolas.