=Insulation, Oil.= Any non-combustible oil may be employed as an insulator to prevent electrical leakage in induction-coils, transformers, and the like. Its principal advantage lies in its being in liquid form, permitting of easy handling. Moreover, if pierced by a spark from a coil, it at once closes again without becoming ignited. A solid insulator, if pierced, is permanently injured. =Insulator.= Any insulating substance or material to prevent the escape of current. The knobs of porcelain or glass to which wires are made fast. =Insulator, Porcelain.= An insulator made of porcelain and used to support a wire. =Intensity.= The intensity or strength of a current is its amperage. The strength of a magnetic field, its power to attract or magnetize. =Internal Circuit.= (_See_ Circuit, Internal.) =Internal Resistance.= (_See_ Resistance, Internal.) =Interrupter.= A circuit-breaker. Any device which breaks or interrupts a circuit. It may be operated by hand or automatically. The vibrator of an induction-coil. The commutators of an armature. =Isolated Plant.= The system of supplying electric energy by independent generating dynamos for each house, factory, or traction line. =Isolation, Electric.= A term applied to “electric sunstroke.” Exposure to powerful arc-light produces effects resembling those of sunstroke. J =Joint.= The point where two or more electric conductors join. =Joint Resistance.= The united resistance offered by a number of resistances connected in parallel. =Jumper.= A short circuit-shunt employed temporarily around an apparatus, lamp, or motor to cut out the current. =Jump-spark.= A disruptive spark excited between two conducting surfaces in distinction from a spark excited by a rubbing contact. K =Kaolin.= A form of earth or product of decomposed feldspar composed of silica and alumina. It is serviceable in insulating compounds. =Kathode.= The terminal of an electric circuit whence an electrolyzing current passes from a solution. It is the terminal connected to the zinc pole of a battery or the article on which the electro-deposit is made. =Key.= The arm of a telegraphic sounder by which the circuit is made and broken. A pivoted lever with a finger-piece which, when depressed, makes contact between a point and a stationary contact on the base. =Keyboard.= A board, or table, on which keys or switches are mounted. A switchboard. =Kilowatt.= A compound unit; one thousand watts; an electric-current measure. Abbreviation, K-W. =Kilowatt Hour.= The result in work equal to the expenditure or exertion of one kilowatt in one hour. =Kinetoscope.= A photographic instrument invented by Edison for obtaining the effect of a panorama or moving objects by the display of pictures in rapid succession--in familiar parlance, “moving pictures.”