sympiesometer

[Greek sympiesis = a compre ion, from sympiezō to pre together, (sym, for syn =with, together, and piezō -to pre ), and metron a measure.) An instrument invented by Mr. Adie, of Edinburgh, Scotland, for measuring the weight of the atmosphere by the compre ion of a column of gas. It consists of a column of oil, supported by atmospheric pre ure, and rising, not like the mercury of the barometer into a vacuum, but against a body of hydrogen gas, which acts like a spring against the column of oil; and as the elasticity of the hydrogen varies with every change of temperature, a movable thermometer scale is attached for making the nece ary corrections. The sympiesometer is graduated by placing it together with a standard barometer and thermometer in a gla ve el, in which the pre ure of the air can be varied at pleasure. The top of the column is marked at the points where the barometer shows 27, 28, 29, 30, 31 inches respectively. The spaces between the marks, coinciding with the inches of mercury, are then subdivided into 100 equal parts each, and the great range makes the instrument valuable for recording minute variations, subject to correction, depending on the variation in the volume of the hydrogen, due to changes of the temperature. A graduated sliding scale a ists in reaching the corrected result. sym-plě-şite, s. [Gr. sym, for syn=together, and plēsiazō -to approach.] Min.: A monoclinic mineral, occurring in tufts of small prismatic crystals in cavities in Siderite (q.v.). Hardne , 2.5; specific gravity, 2.957; luster on cleavage face, pearly, elsewhere vitreous; color, celandine-green. Composition: Supposed to be an arsenate of protoxide of iron.