Spirit Level

A spirit level is an instrument designed to show whether a surface is horizontal, or level, or vertical, or plumb, working through a liquid filled vial containing an air bubble that shows when a surface is properly aligned; alcohol is used rather than water because it will not freeze and offers less friction for the bubble, giving greater accuracy. The instrument is centuries old: the French scientist Melchisedech Thevenot built one before February 2, 1661, a date established through his correspondence with Christiaan Huygens, and within a year he had shared the design with Robert Hooke in London and Vincenzo Viviani in Florence. A later American development came from William B. Fell of Rockford, Illinois, who invented the Fell All Way precision level in 1939, able to measure tilt on more than one axis at once. Spirit levels come in two main forms, tubular levels for measuring along a line and bull's eye levels for leveling a whole plane at once, and in versions adapted for carpenters, masons, bricklayers, surveyors and metalworkers.