=Core-disks.= Disks of thin wire, for building up armature-cores. The usual form of a core is round or cylindrical. A number of thin disks, or laminations, of iron strung upon the central shaft, and pressed firmly together by the end-nuts or keys. This arrangement gives a cylinder as a base on which to wind the insulated wire that forms a part of the armature. =Core-disks, Pierced.= Core-disks for an armature of a motor or dynamo, which have been pierced or bored out around the periphery. Tubes of insulating material, such as fibre, rubber, or paraffined paper, are inserted in the holes and through these the windings of wire are carried. The coils are thus imbedded in the solid mass of iron, and are protected from eddy currents; also they act to reduce the reluctance of the air-gaps. This arrangement is very good, from a mechanical point of view, but in practice its use is confined to small motors only, and dynamos generating under one hundred volts. =Core-disks, Toothed.= Core-disks of an armature or motor where notches are cut from the periphery. When they are locked together, to form the armature-core, the coils of wire lie in the grooves formed by a number of the disks bound together. This construction reduces the actual air-gaps and keeps the coils equally spaced. =Core, Laminated.= The core of an armature, an induction-coil, a converter, or any similar piece of apparatus, which is made up of plates or disks, insulated more or less perfectly from one another by means of mica or paraffined paper. The object of laminations is to prevent the formation of Foucault currents. A core built up of disks is sometimes called a radially laminated core. =Core, Ring.= A dynamo or motor armature-core which forms a complete ring. =Core, Stranded.= The core of a cable, or a conducting core made up of a number of separate wires or strands laid or twisted together. =Core, Tubular.= Tubes used as cores for electro-magnets, and also to produce small magnetizing power. Tubular cores are nearly as efficient as solid ones in straight magnets, because the principal reluctance is due to the air-path. On increasing the current, however, the tubular core becomes less efficient. =Coulomb.= The practical unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second. =Couple.= The combination of two electrodes and a liquid, the electrodes being immersed in the latter, and being acted on differentially by the liquid. This combination constitutes a source of electro-motive force, and, consequently of current, and is called the galvanic or voltaic cell or battery. =Couple, Astatic.=. A term sometimes applied to astatic needles when working in pairs. =Coupling.= The union of cells or generators constituting a battery; the volume of current, or electro-motive force, is thereby increased. =C. P.= An abbreviation for “candle power”; also meaning “chemically pure,” when speaking of chemicals.