Gauge

Gauge is a measuring instrument. A pressure gauge is an instrument for measuring the pressure of a fluid such as the steam in a boiler. The most generally adopted pressure gauge is that known as Bourdon's (q.v.), which admits the fluid into a curved hollow tube of special section, closed at the extreme end. The internal pressure tends to straighten out the tube, which is fixed at the open end so that the closed end is free to move under the action of the internal force. Its motion is communicated to a pointer on a graduated dial and the pressure is thus estimated. Similar in principle is the ordinary vacuum gauge, to measure the degree of vacuum produced in steam-engine condensers, or in air-pump receivers. In this case the hollow tube is connected with the exhausted space; and the external pressure being in this case greater than the internal, the tube will exhibit a reverse action and become more curved. The recording part of the instrument is the same as before.

The Wire Gauge (q.v.) is for the purpose of determining the diameter of wires, and is of much importance in modern electrical work. The simplest form consists of a plate of steel in which slits are cut of various widths. Each slit is numbered, and the diameter of the given wire is expressed by the number of that special slit into which it exactly fits. There are, unfortunately, various systems of numbering, the Birmingham wire gauge (generally termed B.W.G.) being the most widely adopted It would be much more convenient in many ways to give the width of each slit in decimal parts of an inch.

Wind Gauge is an instrument for measuring the intensity of wind-pressure, and is generally of the windmill type, the amount of rotation of a small windmill of special construction giving the average intensity of the wind during a known interval. [Anemometer.]

Rain Gauge (q.v.) measures the number of inches of rainfall in a given period of time, by collecting the rain in a graduated vessel, taking care to prevent loss by evaporation or other causes.