In a telephone exchange or telegraph office a drop shutter annunciator, which falls to call the attention of the operator, notifying him that the line connected to such drop is to be connected to some other circuit.

A push button used for ringing a call bell, sounding a buzzer, working an annunciator and for similar purposes.

A bell rung by pressing a button or otherwise to call the attention of a person in a distant place. They can be classified into a great variety of types according to their uses or construction.

The determination of the law connecting the various indications of an instrument, such as the deflections of the needle of a galvanometer, with the relative causes; in the case of a galvanometer, the strength of the currents or the electro-motive forces producing them directly or indirectly.

Calibration applicable to specially constructed galvanometers, which is unaffected by the proximity of masses of iron or field magnets. Such galvanometers must have a constant controlling field. Such is given by a powerful permanent magnet, whose field is practically unaffected by the causes named. Or else, in place of a controlling field, a spring maybe [...]

The determination of the absolute value of currents producing given deflections in a galvanometer, or in other instruments the determination of corresponding values, as the instrument may be a magnetometer, quadrant electrometer, or other apparatus.

The determination by experiment or calculation of the value of the readings of an instrument, such as a galvanometer or eudiometer. Thus if a tangent galvanometer has its circle graduated in degrees, a table of the value of tangents corresponding to every reading occurring in practice would represent a calibration by calculation. A determination of [...]

A mineral; zinc silicate; formula Zn2 Si 03, crystalline system, Orthorhombic; specific gravity, 3.16-3.9. The crystals often show strong pyroelectric properties.

A tank in which a submarine cable is coiled away on board a cable-laying ship, or in the factory on shore for the purpose of testing or watching its insulation. Sometimes, in order to test it under pressures approximating to those it will be subjected to in practice, the tank is closed and the portion [...]

A wire by which an aerial cable is in part or entirely suspended. The cable, being incapable of sustaining its own weight, is secured by clips or hangers to a wire, strong from pole to pole immediately above it.