The Democratic Press

Professor Bell's new induction balance consists of two flat coils about four inches in diameter and one-half inch in thickness, of insulated copper wire, a battery, a condenser, an interrupter, or circuit breaker, and a telephone. The ends of the primary or inducing coil are connected with the poles of the battery, and in the same circuit are a condenser and a small interrupter, whose vibrating tongue opens and closes the circuit with great rapidity. The ends of the secondary coil in which the current is to be induced are carried to the binding posts of the bell of the telephone. When the connections have all thus been made a secondary coil is laid on a primary or inducing coil, so that their respective circumferences exactly coincide. A circuit breaker is then set in motion, and the rapidly interrupted current through the primary coil induces another current of higher intensity in the secondary coils, and as it does so a loud musical tone is heard in the telephone with which the secondary coil is connected. As long as the circuit is maintained and the circumferences of the two coils are kept in exact coincidence the musical note in the telephone does not change its pitch or intensity. If, however, the experimenter slides the upper coil along an inch or so upon the lower so that their circumferences no longer correspond, the intensity of the musical tone is diminished, and just in proportion as the centers of the flat coils are separated by a greater or less distance the intensity of the musical tone is lessened or increased. By delicate manipulation it is possible to adjust the centers of the overlapping coils at such distance one from another, that a perfect balance is brought about, and when this is the case the telephone marks no sound whatever. As soon as balanced the coils begin to feel the disturbance caused by their approach to the imbedded bullet, the telephone announces the fact by a faint continuous musical note, and this note grows louder and louder and louder until the overlapping parts of the coils are directly above the disturbing metal when the sound reaches its maximum.