=Electrolytic Resistance.= (_See_ Resistance, Electrolytic.) =Electro-magnetic Induction.= (_See_ Induction, Electro-Magnetic.) =Electro-magnetism.= Magnetism created by electric current. That branch of electrical science which treats of the magnetic relations of a field of force produced by a current. =Electro-medical Bath.= A bath provided with connections and electrodes for causing a current of electricity to pass through the body of the patient. =Electrometer.= An instrument used for measuring static electricity. Electrometers are different from galvanometers, since the latter depend on a current flowing through wires to create an action of the magnetic needles. =Electro-motive Force.= Voltage. It may be compared to the pressure of water in hydraulic systems. The unit of electro-motive force is the volt. =Electro-motor.= A term sometimes applied to a current-generator, such as a small dynamo or voltaic battery. =Electro-plating.= (_See_ Plating, Electro.) =Electropoion Fluid.= An acid depolarizing solution for use in zinc-carbon couples, such as the “Grenet” and “Daniell” cells. The bi-chromate-of-potash and sulphuric-acid solution for battery charges is a good example. =Electroscope.= An apparatus for indicating the presence of an electric charge and whether the charge is negative or positive. =Electrostatic Accumulator.= Two conducting surfaces, separated by a dielectric and arranged for the opposite charging of the two surfaces. A faradic or static machine for accumulating frictional electricity is an example. =Electrostatics.= That division of electric science which treats of the phenomena of the electric charge, or of electricity in repose, as contrasted with electro-dynamics or electricity in motion. =Electrotype.= The reproduction of a form of type or engraving by the copper electro-plating process. The original is coated with plumbago and a wax impression taken of it. The face of the negative is made conductive with plumbago or tin dust, then suspended in a copper bath and connected with the current. A film of copper will be deposited on the face of the wax impression. =Element, Chemical.= Original forms of matter that cannot be separated into simple constituents by any known process. There are about seventy in all, but as science advances the list is constantly being revised. New elements are discovered and known ones are being resolved into simpler forms. =Elements of Battery Cell.= (_See_ Battery Cell, Elements of.) =Emergency Switch.= An auxiliary switch used as a controller on a car to reverse the action of the motor. =E-M-F.= An abbreviation for electro-motive force, or voltage. =Equalizer.= A term applied to a wire or bar in electro-magnetic mechanism for equalizing the pressure over a system. =Exciter.= A generator used for exciting the field-magnets of a dynamo. =Extension Call-bell.= A bell connected with a telephone call-bell, and located in another part of a building so as to give a distant summons.