An inert gas that makes up about 1% of the atmosphere.
Ornament consisting of garlands of foliage with figures, fancifully interlaced to form graceful curves and painted, inlaid, or carved in low relief.
Arago Spot
A bright spot that appears in the shadow of a uniform disc being backlit by monochromatic light emanating from a point source.
An artificially-made organic material that forms very long and stiff fibres.
Aramid Fibres
A class of heat-resistant and strong synthetic fibres.
Arbitrary Unit
A unit that is not part of the standardized metric or other system.
A shaft or spindle for holding cutting tools; most usually on a milling machine.
Arbor Press
A hand-operated machine tool designed for applying high pressure for the purpose of pressing together or removing parts.
Part of a circle.
Arc Brazing
A brazing process wherein the heat is obtained from an electric arc formed between the base metal and an electrode.
Arc Cutting
A group of cutting processes in which the cutting of metals is accomplished by melting with the heat of an arc between the electrode and the base metal.
Arc Flash
An electrical explosion that results from a low-impedance connection to ground or another voltage phase in an electrical system.
Arc Furnace
An electric furnace, in which heat is produced by an arc between two electrodes.
Arc Length
The distance between the endpoints of an arc along the path of the circle.
Arc Oxygen Cutting
An oxygen-cutting process used to sever metals by a chemical reaction of oxygen with a base metal at elevated temperatures.
Arc Welding
A group of welding processes in which fusion is obtained by heating with an electric arc or arcs, with or without the use of filler metal.
A series of arches supported by columns or piers, or a passageway formed by these arches.
The inverse of cosine. Note that arccos(A)=cos-1(x).
The inverse of cotangent. Note that arccot(A)=cot-1(x).
The inverse of cosecant. Note that arccsc(A)=csc-1(x).
A curved structural member that spans an opening and is generally composed of wedge-shaped blocks that transmit the downward pressure out laterally.
Arch Bridge
A curved structure that converts the downward force of its own weight, and of any weight pressing down on top of it, into an outward force along its sides and base.
Arch Dam
A dam with an arched shape that resists the force of water pressure; requires less material than a gravity dam for the same distance.
The geological eon covering about 3.9 billion years ago to 2.6 billion years ago.
The geological period from 4.6 billion to 1.0 billion years ago.
Forever to be known for the Archimedean principle: "a body plunged in a fluid loses as much weight as... "
Archimedes Constant
More commonly known as Pi.
Archimedes′ Principle
The buoyant force is equal to the weight of the displaced fluid.
A person who designs all kinds of structures.
Architectural Acoustics
Lists all Architectural Acoustics topics in the Encyclopaedia.
Architectural Acoustics Calculations
Lists all Architectural Acoustics Calculations in the Encyclopaedia
Architectural Acoustics Conversions
Lists all Architectural Acoustics Conversions in the Encyclopaedia
Architectural Acoustics Weblinks
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Architectural Coatings
Coverings such as paint and roof tar that are used on exteriors of buildings.
Lists all Architecture topics in the Encyclopaedia
Architecture Books
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Architecture Calculations
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Architecture Conversions
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Architecture Weblinks
Lists all Architecture Weblinks in the Encyclopaedia
The lowest part of an entablature resting on the capital of a column. Also, the holdings around a doorway.
Defined as 1/60 of a degree.
Arc-Resistance Switchgear
Switchgear designed to withstand the effects of an internal arcing fault, without causing harm to personnel.
The inverse of secant. Note that arcsec(A)=sec-1(x).
Defined as 1/360 of a degree.
The inverse of sine. Note that arcsin(A)=sin-1(x).
The inverse of tangent. Note that arctan(A)=tan-1(x).
A derived SI Unit of area. 1 Are = 100m2
The derived SI unit of area is the m2.
Areal Weight
The weight of fibre per unit area, width times length, of tape or fabric.
A hydrocarbon that contains at least one aromatic ring.
Naturally occuring Silver Sulphide. An important ore of silver.
Latin for silver, hence the symbol Ag.


A semiessential or conditionally essential amino acid in mammals.

An inert gas that makes up about 1% of the atmosphere.
A Greek philosopher who stressed the importance of direct observations in securing facts and data.
The type of mathematics that studies how to solve problems involving numbers, but not variables.
Arithmetic Coding
Arithmetic coding removes this restriction by representing messages as intervals of the real numbers between 0 and 1.
Arithmetic Error
As error that occurs when discarding least significant bits of a fixed-point arithmetic operation.
Arithmetic Mean
The arithmetic mean of n numbers is the sum of the numbers divided by n.
Arithmetic Operators
Symbols and signs used in mathematics.
Arjuna Asteroids
Asteroids that orbit the Sun in a near circular path and are no more than 100m in diameter.
Arko Metal
A brass made with 80% copper and 20% zinc.
In a relay, the movable portion of the relay. The windings in which the output voltage is generated in a generator or in which input current creates a magnetic field that interacts with the main field in a motor.
Armature Air Gap
The air space between the stationary and rotating parts of a motor or generator, through which magnetic lines of force pass.
Armature Losses
Copper losses, eddy current losses, and hysteresis losses that act to decrease the efficiency of armatures.
Armature Reaction
The effect in a dc generator of current in the armature creating a magnetic field that distorts the main field and causes a shift in the neutral plane.
Armstrong, Edwin Howard
American electrical engineer and inventor of the modern frequency modulation radio.
Aromatic compounds have strong, characteristic odors.
Aromatic Compound
A compound containing an aromatic ring.
Aromatic Ring
An exceptionally stable planar ring of atoms with resonance structures that consist of alternating double and single bonds, e. g. benzene.
Abbreviation of Advanced Research Projects Agency Network.
Arrhenius Equation
Variation of rate constant with temperature for several elementary reactions.
Arrhenius, Svante August
Swedish physicist and chemist who originated the modern theory of ionization of electrolytes. Received the Nobel Prize for chemistry in 1903.
Absence of rhythm,eg in heart beat.
Arrol, Sir William
Scottish engineer who most notably built the Tay Rail Bridge in 1887, Forth Rail Bridge in 1890 and Tower Bridge in 1894.
A brittle, crystalline solid which tarnishes readily in air and burns in oxygen.
Arsenic III Oxide


White crystalline solid, used as an opacifier in glazes.

Arsenic V Oxide


White solid.

Arsenical Bronze
An alloy of copper and arsenic in addition to other metals.

Arsenical Copper
An alloy of copper and arsenic in addition to other metals.
Old name for Hydrogen Arsenide.
A blood vessel that carries blood away from the heart. All arteries, except for the pulmonary artery, contain oxygen.
Artesian Well
A well in which the water in the aquifer is under pressure that raises the water above the point that the well first encounters it.
Articulated Piston
Two-piece pistons incorporating an entirely separate piston crown or dome with a separate skirt.
Articulation Class
A measure for rating the speech privacy performance of a ceiling in an open plan environment.
Articulation Index
A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded.
Articulation Loss of Consonants
The measured percentage of Articulation Loss of Consonants by a listener.
Articulation Score
A subjective measure of the intelligibility of a voice system in terms of the percentage of words correctly understood over a channel perturbed by interference.
Artificial Gravity
Gravity established within a space vehicle by rotation or acceleration.
Artificial Intelligence
Field of computer science concerned with the concepts and methods of symbolic inference by computer, and the symbolic representation of the knowledge to be used in making inferences.
Artificial Reverberation
Reverberation generated by electrical or acoustical means to simulate that of concert halls, etc.
Artificial Satellite
A man made satellite.
Artificial Transmission Line
An LC network that is designed to simulate characteristics of a transmission line.
A molecular fragment or group attached to a molecule by an atom that is on an aromatic ring.