BAROMETER

an instrument for | “< measuring the preesure of the air. In its simplest form it consists of a vertical gla | N¢ tube about 33 inches in length, closed at | ha one end. This is filled with mercury, and | ki: inverted, with its open end under the | — surface of more of the same liquid contained | in! in s shallow ve el. The mercury in the | of tube falls cntil it reaches a point ebout | ab $0 inches above the mercury in the cup.| | The distance from the surface of the/|d. liquid in the cup to the top of the mercury | ms in the tube is called the height of the | Ms barometer. A height of30inches indicates| | an atmospheric pre ure of fifteen pounds | st< to the square inch, and a variation of one | the inch in the height marks a change of half | 18 @ pound in the pre uro. In the Syphon | lit Barometer the open end of the tube is| pu bent into the shape of tho letter U, and | an the sop is dispensed with, Also see! Re Aneroid. an [s. 64]