All measuring devices can be considered tools of some sort, but the basic tools used in earlier times were used to measure distances, determine angles, level or vertical surfaces, squareness, or to mark a specific point on a surface.

Levels

A level is an instrument used to determine whether an object is either parallel (level) to the earth's surface (horizontal), or perpendicular (plumb) to it. The most popular level today is the Spirit Level, which took almost 200 years to gain acceptance after its invention in 1666 in France.

The Spirit Level consists of a clear, slightly curved tube, nearly filled with a liquid, usually alcohol, set in a long piece of wood or metal in such a way that when the level is perfectly horizontal, the bubble of air which remains in the clear tube is centered between two marks in the tube. The less the curvature the more sensitive the level. Many levels, especially those used by carpenters, were rather ornate in style.

The Spirit Level is so called because its inventor, Thevenove, used wine in the tube.

Bobs

Leveling with a plumb bob dates back to the Egyptians. It consists of hanging a weight on a string at right angles to a reference horizontal surface or line. Gravity forces the string to hang vertically.

Bobs are found in all kinds of shapes and weights. The biggest variation is in weight, ranging from 1 1/2 ounces to 5 pounds. This difference is required to satisfy the various "drop" distances and to minimize any tendancy of the bob to be displaced by a stiff breeze. The bob is often used with surveyors instruments, hanging directly beneath the sighting telescope to establish a positioning mark upon the surface of the earth.

| Home | Exhibit Guide |

This page last updated: August 5, 2002 Original content: Copyright © 2000, 2001 Museum of American Heritage