GAUGE

( Ang. S. SaeSSian, to bind or confine.) In Architecture, the length of a slate or tile below the lap; also the measure to which any substance is confined. Plasterers use the word to signify the greater or le quantity of plaster of Paris used with the common plaster to accelerate its setting. Gage. In Physics, an instrument or apparatus for measuring the state of a phenomenon. Gage of the air pump is merely a barometer communicating with the inside of the receiver, which marks, in the usual manner, the pre ure of the air within the receiver by the height of the equiponderant column of mercury, and consequently shows the degree to which the air is rarefied. A short barometer may be employed for this purpose; but in this case it will not be aflFected till the rarefaction of the air has been carried so far as to correspond with the length of the tube. An instniment for the same purpose, but on a different principle, was invented by Smeaton, and from its form called the pear-gage. It is a ve el suspended in the receiver, and exhausted to the same degree; but when the rarefaction is carried as far as intended, the open orifice of the gage is let down into a ve el containing mercury, which, on the readmi ion of the air, is forced up into the pear, and the degree of rarefaction is judged of by the quantity of mercury introduced. The idea is ingenious; but the indications given by this instrument are not correct. For wind-gage, see ANEMOMEfER; water-gage, see Hydrometer. [s. 495]