Device for establishing a horizontal plane. It consists of a small, sealed glass tube containing liquid and an air bubble; the tube is fixed horizontally in a block or frame with a smooth lower surface. When the bubble is in the middle of the glass tube, the device is on a level surface; adjustment to the horizontal is indicated by movement of the bubble. The glass tube is slightly bowed, and the level's sensitivity is proportional to the radius of curvature.
This entry comes from Encyclopædia Britannica Concise.
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