=Power-unit.= The unit of electric power is the volt-ampere or watt. =Pressure, Electric.= Electro-motive force or voltage. =Primary.= A term used to designate the induction-coil in an induction-apparatus or transformer. It is an abbreviation for primary coil. =Primary Battery.= (_See_ Battery, Primary.) =Prime Conductor.= (_See_ Conductor, Prime.) =Push-button.= A switch for closing a circuit by means of pressure applied to a button. The button is provided with a spring, so that when pushed in and released it flies back, reopening the circuit. =Pyrogravure.= A process of engraving by the use of platinum points heated to redness by the electric current. Q =Q.= Abbreviation or symbol for electric quantity. =Quadrant.= The quarter of a circle or of its circumference. =Quadruple Circuit.= (_See_ Circuit, Quadruple.) =Quantity.= The term is applied to express arrangements of electrical connections for giving the largest possible amount of current. =Quantity, Electro-magnetic.= The electro-magnetic current measured by its intensity for a second of time. =Quick-break.= A break affected in an electric current by the employment of a quick-break switch. =Quickening.= The amalgamating of the surface of a metallic object before electro-plating it with silver. This secures better adhesion of the deposit, and is done by dipping the article into a solution of mercurial salts--one part of mercuric nitrate to one hundred parts of water. R =Radiant Energy.= Energy existing in the luminiferous ether and exercised in wave transmission, creating light or sound. Radium possesses the highest form of radiant energy. =Radiate.= To emit or send out in direct lines from a point or points, as radiating heat, light, or sound. The radiations are sent out in all directions from a central point, just as a stone thrown in a pond of still water will radiate waves or ripples from the central point. =Radiation.= The travelling or motion of ether waves through space. =Radiator, Electric.= A series of plates or wire-coils heated by current. They radiate heat and so warm the surrounding air. =Radiograph.= A photographic picture taken by the X-ray process. =Receiver.= In telephony or telegraphy, an instrument for receiving the message as distinguished from the instrument sending or transmitting the message. The telephone piece held to the ear is the receiver. =Receiving End.= The end of a line where the operative currents are received, as opposed to the end at which they are transmitted. =Receptacle.= A device for the installation of an attachment or extension plug. Used in connection with electric-lighting circuits. =Recoil Kick.= Reaction resulting from a disruptive discharge. =Recorder.= In telegraphy, the receiving apparatus for recording the dot-and-dash signals on a strip or tape of paper.