Chinese English

A description, explanation, table of SYMBOLS, and other informa­tion, printed on a MAP or CHART to provide a better understanding and interpreta­tion of it. The TITLE of a MAP or CHART formerly was conside­red part of the legend, but this usage is obsolete.

A plane, convex, or concave combination of glass or transparent material surfaces adapted for changing the direction of LIGHT RAYS to enlarge or reduce the apparent size of objects. See ACHROMATIC LENS, APOCHROMATIC LENS, ANALLACTIC LENS, OBJECTIVE LENS, EYEPIECE, LENS ELEMENT, LENS SYSTEM, MAGNIFYING GLASS.

一种平面的，凸状或凹状玻璃或透光物质制成的组合镜，用于改变光的方向以放大或缩小物体的尺寸。参见achromatic lens（消色差透镜）, apochromatic lens（复消色差透镜）, objective lens（物镜）, eyepiece（目镜）, lens element（透镜件）, lens system（透镜系统）, magnifying glass（放大镜）。

A horizontal plane or line; especially, such a plane taken as a basis for the measurement of ELEVATI­ON. See SEA LEVEL, MEAN SEA LEVEL, HALF TIDE LEVEL, STILL WATER LEVEL. A level tract of land; a stretch of country ap­proxi­mately horizontal and unbroken by ELEVATIONS. In SURVEYING and LEVELLING, either a SPIRIT LEVEL or a LEVELLING INSTRUMENT.

水平面或水平线；特别是作为测量高程基础的平面。参见sea level（海平面）, mean sea level（平均海平面）, half tide level（半潮面）, still water level（静止水面）。 陆上广阔的水平地面；一片近似水平且未被高地截断的土地。 在测量和水准测量中，指水准器或水平仪。

A SPIRIT LEVEL attached to the plate of a surveying instrument for the purpose of levelling the graduated CIRCLE or, in­directly, making the VERTICAL AXIS truly vertical.

A small closed vessel of glass (vial), having the inside surface of its upper part curved in form; the vessel is nearly filled with a fluid of low viscosity (alcohol or ether), enough free space being left for the formation of a bubble of air and gas, which will always assume a position at the top of the vessel. There are two types of spirit levels used in SURVEYING: one has the curved surface spherical in form, producing a bubble of circular outline; and is properly called a circular level (also universal level or bull's eye level). The other and much more generally used type has a vessel in the form of circular tube, the longitudinal axis of which is also circular in form. It is the type usually referred to when the term 'spirit level' is used. The spirit level is also called spirit bubble or sensitive bubble.

一种小型密封的容器（玻璃管），其内部表面上部是弯曲的，容器填充了低粘度的液体（酒精或乙醚），在容器顶部的位置上保留了足够形成气泡的自由空间，应用于测量方面有两种类型水准器，一种是球形曲面，产生圆形气泡，称为圆水准器（也称通用水准器或气泡圆水准器）。另一种是大多数情况下使用的类型，容器是一圆形管，其纵向轴也呈圆形。日常所称“水准器”即指这一类型。水准器亦称spirit bubble （水准气泡）或sensitive bubble（灵敏气泡）。

A SPIRIT LEVEL so mounted that it can be placed above and parallel with the HORIZONTAL AXIS of a surveying or astronomical instrument, and so supported that it can be used to measure the INCLINATION OF THE HORIZONTAL AXIS to the plane of the HORI­ZON. Generally, its mounting has supports in the form of inverted eyes which rest directly upon the pivots on which the TELESCOPE of the instrument rotates.