A = Area of piston in square inches. P = Average pressure of steam in lbs. per square inch. R = Number of revolutions per minute. S = Length of stroke in feet (if in inches, × 33,000 by 12). The French “force cheval” represents 32,560 foot pounds. _Horse-Power of Water._—Indian Government rule, 15 cube feet per second falling through 1 foot = 1 HP. _Indicator Diagram._—The drawing produced by an instrument which is fixed to the cylinder of a steam-engine for the purpose of ascertaining its duty. _Induction._—The name given to effects produced out of a force-exerting body or out of the circuit to which the force is directly applied. A current in a wire induces currents in other conductors parallel to it. _Inertia._—The resistance to change of state of rest or motion. _Insulators._—Bodies possessing high electrical resistance. All insulating substances, however, allow some electricity to pass. _Intensity._—The old term for the properties now described as E. M. F. and potential. _Joule_, also called _Joulad_ (W).—The Unit of heat or work, it has also been applied to the mechanical equivalent of heat, 772 foot lbs. _Kilowatt._—One thousand watts. _Knot._—The geographical and nautical mile. _Leads._—Terms usually applied to copper conductors. _Magnetism._—A condition which can be highly developed in iron and steel, by electric action or otherwise. _Measurement._—See Units. _Metre._—The French standard of length = 3·28 feet. _Meg Ohm._—The prefix meg signifies a million. _Millimetre._—The thousandth part of a metre. _Milliampère._—The thousandth of an ampère. _Mica-foil._—The fusible portion of a Hedges cut-out. _Multiple Arc._—Galvanic cells or dynamos connected parallel, or lamps so arranged that each furnishes a separate path for the current. _Negative._—In a machine the wire returning from the lamp. In a galvanic battery the copper, carbon, or platinum plate. Sign -. _Nigger._—An American term used to denote an electrical fault. _Ohm._—The Unit of resistance. A volt divided by an ampère. _Ohm’s Laws._—Laws, investigated by Ohm, regulating electrical current magnitudes. Calling the current C, electro-motive force E, and resistance R: the expression is Current E. M. F. Resistance. E E C = ——, amps. E = C × R, volts. R = —— ohms. R C (See Electrical Measurements.) _Osmose._—The process of diffusion of liquids through a porous division. _Paraffin._—An insulating substance much used in telegraphic work. _Plummer Block._—The bearing on which a shaft revolves.