=Alternator.= An electric generator-dynamo supplying an alternating current. =Amalgam.= A combination of mercury with any other metal. =Amalgamation.= The application of mercury to a metal, the surface of which has been cleansed with acid. Mercury will adhere to all metals, except iron and steel, and particularly to zinc, which is treated with mercury to retard the corrosive action of acid on its surface. =Amber.= A fossil resin, valuable only in frictional electric experiments. Most of it is gathered on the shores of the Baltic Sea between Königsberg and Memel. It is also found in small quantities at Gay Head, Massachusetts, and in the New Jersey green sand. When rubbed with a cloth it becomes excited with negative electricity. =Ammeter.= The commercial name for an ampere-meter. An instrument designed to show, by direct reading, the number of amperes of current which are passing through a circuit. =Ampere.= The practical unit of electric current strength. It is the measure of the current produced by an electro-motive force of one volt through a resistance of one ohm. =Ampere-currents.= The currents theoretically assumed to be the cause of magnetism. =Ampere-hour.= The quantity of electricity passed by a current of one ampere in one hour. It is used by electric light and power companies as the unit of energy supplied by them, and on which they base their reckoning for measuring the charges for current consumed. =Ampere-ring.= A conductor forming a ring or circle. Used in electric balances for measuring current. =Animal Electricity.= A form of electricity of high tension generated in certain animal systems--the Torpedo, Gymnotus, and Célurus. The shocks given by these fish, and particularly the electric eel, are often very severe. =Annealing.= The process of softening yellow metals by heating them to a cherry redness, then allowing them to cool gradually in the air. Electric annealing is done by passing a current through the body to be annealed, and heating it to redness; then allowing it to cool gradually. =Annunciator.= An apparatus for giving a call from one place to another, as from a living-room to a hotel office, or for designating a window or door that may have been opened when protected by a burglar-alarm. =Annunciator-drop.= The little shutter which is dropped by some forms of annunciators, and whose fall discloses a number or letter, designating the location from which the call was sent. =Anode.= The positive terminal in a broken, metallic, or true conducting circuit. The terminal connected to the carbon-plate of a battery, or to its equivalent in any other form of electric generator, such as a dynamo or a voltaic pile. The copper, nickel, gold, or silver plates hung in an electro-plating bath, and from which the metal is supplied to fill the deficiency made by the electro-deposition of metal on the kathode or negative object in the bath.