A
spirit level or
bubble level is an
instrumentIn the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
designed to indicate whether a surface is
horizontalIn geometry, physics, astronomy, geography, and related sciences, a plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point— in other words, if apparent gravity makes a plumb bob hang perpendicular to the plane at that point.In...
(level) or
verticalIn astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
(
plumbA plumb-bob or a plummet is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb-line....
). Different types of spirit levels may be used by
carpenterA carpenter is a skilled craftsperson who works with timber to construct, install and maintain buildings, furniture, and other objects. The work, known as carpentry, may involve manual labor and work outdoors....
s, stonemasons,
bricklayerA bricklayer or mason is a craftsman who lays bricks to construct brickwork. The term also refers to personnel who use blocks to construct blockwork walls and other forms of masonry. In British and Australian English, a bricklayer is colloquially known as a "brickie".The training of a trade in...
s, other building trades workers, surveyors,
millwrightA millwright is a craftsman or tradesman engaged with the construction and maintenance of machinery.Early millwrights were specialist carpenters who erected machines used in agriculture, food processing and processing lumber and paper...
s and other metalworkers, and in some
photographicPhotography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
or
videographicVideography refers to the process of capturing moving images on electronic media even streaming media). The term includes methods of video production and post-production...
work.
Original spirit levels had two
bananaBanana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
-shaped curved glass
vialA vial is a relatively small glass vessel or bottle, especially used to store medication as liquids, powders or in other forms like capsules. They can also be sample vessels; e.g., for use in autosampler devices in analytical chromatography.The glass can be colourless or coloured, clear or amber...
s at each viewing point and were much more complicated to use. In the 1920s, Henry Ziemann invented the modern level with a single vial. These vials, common on most ordinary levels today, feature a slightly curved glass tube which is incompletely filled with a liquid, usually a colored
spiritAqua vitae, or aqua vita, is an archaic name for a concentrated aqueous solution of ethanol. The term was in wide use during the Middle Ages, although its origin is undoubtedly much earlier having been used by Saint Patrick and his fellow monks to refer to both the alcohol and the waters of baptism...
or
alcoholIn chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, leaving a
bubbleA bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...
in the tube. At slight inclinations the bubble will travel away from the center position, which is usually marked in some manner.
Alcohols such as
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
are often used rather than water for a variety of reasons. Alcohols generally have very low
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and
surface tensionSurface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
, which allows the bubble to travel the tube quickly and settle accurately with minimal interference with the glass surface. Alcohols also have a much wider liquid temperature range, and won't break the vial as water could due to ice expansion. A colorant such as
fluoresceinFluorescein is a synthetic organic compound available as a dark orange/red powder soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications....
, typically yellow or green, may be added to increase the visibility of the bubble.
Some spirit levels are capable of indicating the level of a surface between horizontal and vertical to the nearest
degreeA degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
. An extension of the spirit level is the
bull's eye levelA bull's eye level is a type of spirit level that allows for the leveling of planes in two dimensions - both the 'pitch' and 'roll' in nautical terms. Standard tubular levels only consider one dimension...
: a circular, flat-bottomed device with the liquid under a slightly convex glass face which indicates the center clearly. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube. The most sophisticated spirit levels are guaranteed accurate to five-ten-thousandths (.0005) of an horizontal inch at the center per vertical inch at either end. Where a spirit level must also be usable upside-down, the banana-shaped tube is replaced by a barrel-shaped tube. The upper internal surface of the tube is thus always of an appropriate shape.
Checking and adjustment
To check the accuracy of a simple carpenter's type level (i.e. whether the level indicates that a truly horizontal surface is, in fact, level), it is placed on a flat and approximately level surface, and the reading on the bubble tube is noted. This reading indicates to what extent the surface is parallel to the horizontal plane, according to the level, which at this stage is of unknown accuracy. The spirit level is then rotated through 180 degrees in the horizontal plane, and another reading is noted. If the level is accurate, it will indicate the same magnitude of orientation with respect to the horizontal plane. A difference implies that the level is inaccurate and must be adjusted.
Adjustment of the spirit level is performed by successively rotating the level and moving the bubble tube within its housing to take up roughly half of the discrepancy, until the magnitude of the reading remains constant when the level is flipped. Note that a perfectly horizontal surface is not required.
A similar procedure is applied to more sophisticated instruments such as a surveyor's level or a
theodoliteA theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
and is a matter of course each time the instrument is set up. In this latter case, the plane of rotation of the instrument is levelled, along with the spirit level. Furthermore this is done in two horizontal
perpendicularIn geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
directions.
Types of level
There are different types of spirit levels for different uses:
- Surveyor's leveling instrument
- Carpenter's level (either wood, aluminium or composite materials)
- Mason's level
- Torpedo level
- Post level
- Line level
- Engineer's precision level
- Electronic level
- Inclinometer
An inclinometer or clinometer is an instrument for measuring angles of slope , elevation or depression of an object with respect to gravity...
- Slip or Skid Indicator
A spirit level is also usually found on the head of
combination squareA combination square is a tool used for multiple purposes in woodworking, stonemasonry and metalworking. It is composed of a ruled blade and one or more interchangeable heads that may be affixed to it...
s.
Surveyor's leveling instrument
Tilting level,
dumpy levelA dumpy level, builder's auto level, leveling instrument, or automatic level is an optical instrument used to establish or check points in the same horizontal plane...
or
automatic level are terms used to refer to types of
leveling instruments as used in
surveyingSee Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
to measure height differences over larger distances. It consists of a spirit level in the above sense, mounted on a telescope containing cross-hairs, itself mounted on a
tripodA tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. The word comes from the Greek tripous, meaning "three feet". A tripod provides stability against downward forces, horizontal forces and moments about the...
. The observer reads height values off two staffs, one 'behind' and one 'in front', to obtain the height difference between the ground points on which the staffs are resting. Starting from a point with a known (absolute)
elevationThe elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....
, by repeating 'behind', 'front' and intermediate 'front' readings, (relative) height differences can be measured cumulatively over large distances and elevations can be calculated of intermediate points.
See: Spirit leveling
Carpenter's level
A traditional carpenter's spirit level looks like a short plank of wood and often has a wide body to ensure both stability, and that the surface is being measured correctly. Embedded in the middle of the spirit level is a small window where the bubble and the tube is mounted. Two notches (or rings) designate where the bubble should be if the surface was level. Often an indicator for a 45 degree inclination is included.
Line level
A line level is a level designed to hang on a builders string line. The body of the level incorporates small hooks to allow it to attach and hang from the string line. The body is lightweight, so as not to weigh down the string line, it is also small in size as the string line in effect
becomes the body; when the level is hung in the center of the string, each
leg of the string line extends the levels plane.
Engineer's precision levels
An engineer's precision level permits leveling items to a greater degree of accuracy than a plain spirit level. They are used to level the foundations, or beds of machines to ensure the machine can output workpieces to the accuracy pre-built in the machine.
History
The spirit level was invented by
Melchisedech ThevenotMelchisédech Thévenot was a French author, scientist, traveler, cartographer, orientalist, inventor, and diplomat...
(born in either 1620 or 1621; died 1692). Thevenot was an amateur scientist and patron of many scientists and mathematicians. He was wealthy and well-connected, later becoming the Royal Librarian to King
Louis XIV of FranceLouis XIV , known as Louis the Great or the Sun King , was a Bourbon monarch who ruled as King of France and Navarre. His reign, from 1643 to his death in 1715, began at the age of four and lasted seventy-two years, three months, and eighteen days...
. Thevenot invented the instrument some time before February 2, 1661. This date can be very accurately established from Thevenot's correspondence with scientist
Christiaan Huygens. Within a year of this date the inventor circulated details of his invention to others, including
Robert HookeRobert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
in
LondonLondon is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
and
Vincenzo VivianiVincenzo Viviani was an Italian mathematician and scientist. He was a pupil of Torricelli and a disciple of Galileo.-Biography:...
in
FlorenceFlorence is the capital city of the Italian region of Tuscany and of the province of Florence. It is the most populous city in Tuscany, with approximately 370,000 inhabitants, expanding to over 1.5 million in the metropolitan area....
. It is occasionally argued that these bubble levels did not come into widespread use until the beginning of the eighteenth century, the earliest surviving examples being from that time, but
Adrien AuzoutAdrien Auzout was a French astronomer.He was born in Rouen, France, the son of a clerk in the court of Rouen. His educational background is unknown. In 1664–1665 he made observations of comets, and argued in favor of their following elliptical or parabolic orbits...
had recommended that the Académie Royale des Sciences take "levels of the Thevenot type" on its expedition to
MadagascarThe Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
in 1666. It is very likely that these levels were in use in France and elsewhere long before the turn of the century.
Thevenot is often confused with his nephew, the traveler
Jean de ThevenotJean de Thévenot was a French traveller in the East, who wrote extensively about his journeys. He was also a linguist, natural scientist and botanist....
(born 1633; died 1667). There is evidence to suggest that both Huygens and Hooke later laid claim to the invention, although only within their own countries.
See also
- Laser line level
A laser line level is a tool combining a spirit level and/or plumb bob with a laser to display an accurately horizontal or vertical illuminated line on a surface the laser line level is laid against....
- Physical geodesy
Physical geodesy is the study of the physical properties of the gravity field of the Earth, the geopotential, with a view to their application in geodesy.-Measurement procedure:...
- Theodolite
A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
- Plumb-bob
A plumb-bob or a plummet is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb-line....
- Plumb line
- Plumb Site
Plumb Site is a proprietary improvement, and a trademark under that spelling, for a spirit level with a viewing mirror to make it easier to use when setting verticals....
- Turn and bank indicator
In aviation, the turn and bank indicator shows the rate of turn and the coordination of the turn. The rate of turn is indicated from a rate gyroscopically and the coordination of the turn is shown by either a pendulum or a heavy ball mounted in a curved sealed glass tube. No pitch information is...
External links