balance-barometer

Century Dictionary and Cyclopedia

1. n. A barometer consisting of a beam balanced on a pivot, and formed, on opposite sides of the pivot, of materials differing greatly in specific gravity. The bulks of the parts on either side of the fulcrum, and consequently the volumes of air displaced by them, thus differ greatly. If the air increases in density, its effective buoyancy on the more bulky arm considerably exceeds its effect upon the smaller; the former therefore rises. If the air becomes lighter, the reverse happens. The vibrations are noted upon a scale.