Spirit levels are used in surveying, carpentry, construction and other professions to identify whether a surface is horizontal or vertical. In their early days, they included curved, glass vials with continuous inner-diameter at each viewing point. The vials were partially filled with liquid – usually alcohol or a coloured sprit – leaving a bubble in the tube. The vials’ subtle upward curve caused the bubble to rest in the middle, at the highest point. The bubble reacted to any inclination by moving away from the center position.
Alcohols such as ethanol are often used in spirit levels, due to their low surface tension and viscosity, which allows the bubble to move quickly through the tube and settle accurately, with minimal interference.
The bull’s eye level is a circular, flat-bottomed device with liquid underneath a convex glass face, with a circle at the center. Unlike a standard level, a bull’s eye level can be used to level a surface across a plane – rather than only in the direction of the tube.
The sprit level was invented by Melchisedech Thevenot, a wealthy amateur scientist and royal librarian to Louis XIV of France. Examination of correspondence between Thevenot and scientist Christiaan Huygens has revealed that the spirit level was invented at some point before February 2, 1661. Thevenot quickly released a description of his creation to others around Europe, including Vincenzo Viviani, in Florence, and Robert Hooke, in London. Exactly when use of the spirit level in land surveys and other projects became widespread remains unclear, with some arguing that they did not gain popularity until the 18th century, since it is from this period that the oldest surviving examples date. However, there are records of the Academie Royale des Sciences being advised to take “levels of the Thevenot type” on their expedition to Madagascar, in 1666.
The modern level with a single vial was invented by Henry Ziemann, in the 1920s and, in 1939, William B. Fell created the Fell All-Way precision level, in Rockford, Illinois. This bull’s eye level could be positioned on a machine bed and display tilt on the x-y axes, making it unnecessary to rotate the level 90 degrees. Compared to previous designs, Fell’s level was remarkably accurate, and set a new standard of .0005 inches per foot resolution.
Production of the Fell All-Way precision level ceased in around 1970, and was resumed in the ‘80s by Thomas Butler Technology, in Rockford, Illinois, before finally ending in the ‘90s. The spirit level remains an important tool for surveying and various other industries, and has been incorporated into the design of a number of other tools. The dumpy level, which is used to measure height differences over larger distances, often features an inbuilt spirit level. It was invented in 1832, by English civil engineer, William Gravatt. Commissioned to examine a railway route from London to Dover, he devised the dumpy level as a more mobile and easier-to-use alternative to the Y level.