BAROM,'ETER, n. [Gr.weight, and measure.]

An instrument for measuring the weight or pressure of the atmosphere, consisting of a glass tube,hermetically sealed at one end, filled with quicksilver, well defecated and purged of air, and inverted in a basin of quicksilver. A column of quicksilver is then supported in the tube, of equal weight with the incumbent


atmosphere. This instrument was invented by Torricelli, of Florence, in 1643. Its uses are to indicate changes of weather, and to determine the altitude of mountains, by the falling and rising of the mercury. For this purpose,the tube is fixed to a graduated scale, so that the smallest variation in the column is visible.