The ring C has its contact finger connected by a wire L with one end of a primary coil M, while the other terminal has a wire N which goes to one terminal of the interrupter G. The other outlet of the interrupter is connected up with the contact finger of the other collector ring D. This contact finger also has a wire connection P with one terminal of a condenser Q, the other end of the condenser being connected with the wire N, running from the primary coil M. THE SECONDARY COIL.--The secondary, or high tension coil R, has one end grounded, which means that it is connected up with the metal of the engine, and the other terminal is connected by a wire T, with the finger J on the distributer disk. In operation, we will assume that the current leaves the armature over the wire E; it has two paths, one through ring D, wire O, and interrupter G, back to the other wire F of the armature; or, after passing the ring D it may pass over O, to the interrupter, then through wire N, primary coil M, and wire L, back to the armature. OPERATION OF SYSTEM.--The revoluble disk of the interrupter G is so arranged that when the armature has the greatest current intensity it is opened by its turning movement, so that the current is compelled to take the last named course through the primary coil M, and at the same time a certain portion of the current is absorbed by the condenser Q. This intense charge of the current in the primary induces a high tension current in the secondary coil R, and the result is that the current from the secondary goes through the wire T to the finger J, and from the finger J to the contact plate K, and to the particular spark plug which happens to be connected up by one of the wires U with that plate. THE SPARK GAP.--The current in leaping over the gap made by the spark plug, goes through the engine metal to the other end of the secondary coil R, at the place indicated by S. It should be understood that the coils M R are in a separate box, and usually placed in a convenient position in the machine. The diagram illustrating the foregoing, is designed merely to show in a simple manner, how the different mechanical and electrical parts are connected up together. FUNCTION OF THE INTERRUPTER.--The interrupter G, while placed in the primary circuit, necessarily controls not only the primary, but also the secondary circuit. It should not be confounded with the distributer to which the wire T runs from the secondary coil. The office of the interrupter is to break the primary circuit of the magneto at a time when a spark is required, and the duty of the distributer is to have its finger J in such a position at that particular time as to make the connection in the secondary circuit with the particular spark plug which requires a spark. VIBRATORY COILS.--The secondary coil may be so constructed that it will give only a single spark at each impulse, or a plurality of them, and many argue that the latter is more efficient for that reason.