时间：2011-03-11 23:13来源：蓝天飞行翻译 作者：admin 点击：次
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meniscus. The shape of the top of a column of liquid caused by surface tension. Water wets the inside of a glass tube, and capillary action pulls the water up the sides of the tube. Surface tension causes the meniscus of water to be concave. Mercury does not wet the glass, so surface tension causes mercury to have a convex meniscus. When reading a barometer or manometer using a column of liquid in front of a calibrated scale, read the height of the column at a point tangent to the meniscus rather than from the edge of the liquid on the glass. meniscus lens (optics). A simple lens having one concave and one convex side. If the convex side has a longer focal length than the concave side, the lens is a diverging lens. But if the concave side has the longer focal length, the lens is a converging lens. mensuration. The act of measuring or computing lengths, areas, volumes, and angles of various geometric shapes or quantities. Mercator projection (navigation). The projection used for map making in which the meridians of longitude and parallels of latitude are straight, parallel lines. The distance between each meridian of longitude is the same, but the parallels of latitude are close together near the equator and become increasingly farther apart as they near the poles. The shape and size of land masses near the poles are greatly distorted on a map drawn on a Mercator projection. mercerize. A treatment given to cotton thread to make it strong and lustrous. The thread is stretched while it is soaked in a solution of caustic soda. Mercerized thread has a sheen similar to silk, it is stronger and more pliable than untreated thread, and it accepts dye more readily. mercury. A silvery-white, poisonous, metallic chemical element that is liquid at room temperature. Mercury’s symbol is Hg, its atomic number is 80, and its atomic weight is 200.59. Mercury is heavy (more than 13 times as heavy as water), is a good conductor of electricity, and readily unites with other chemical elements. It is used in thermometers to measure temperature by the amount it expands or contracts as temperature changes. It is also used in barometers to determine the pressure of the atmosphere by measuring the height of the column of mercury the atmospheric pressure supports. mercury barometer. An instrument used to measure atmospheric pressure. A glass tube about one meter long, with one end closed and the other end open, is filled with mercury, and the open end is submerged in a bowl, or cistern, of mercury. The mercury in the tube will drop down, leaving a vacuum above the mercury in the closed end. Atmospheric pressure pressing down on the mercury in the bowl holds the mercury up inside the tube. The height of the top of the mercury in the tube above the level of the mercury in the bowl is an accurate measure of the amount of pressure produced by the weight of the atmosphere. Standard atmospheric pressure at sea level holds the mercury up in the tube to a height of 760 millimeters, or 29.92 inches. |
