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Glossary

Key terms introduced across the archive's entries, gathered in one place for quick reference.

A

Additive manufacturing
The general term for building a physical object by adding material layer by layer, as opposed to removing material through cutting or machining. — see “The Development of 3D Printing”
Airfoil
The curved cross-sectional shape of a wing, designed to generate lift as air flows over and under it. — see “The Airplane and the Development of Controlled Flight”
Amplification
The process of increasing the strength of an electrical signal, one of the core functions performed by transistors and earlier vacuum tubes. — see “The Transistor and the Miniaturization of Electronics”
Analog signal
A continuously varying electrical signal that directly mirrors the pattern of the sound wave it represents, as opposed to coded digital pulses. — see “The Telephone and the Evolution of Voice Communication”
Anode
The electrode in a battery that releases electrons during discharge; in a lithium-ion cell, typically a carbon-based material such as graphite. — see “The Development of Lithium-Ion Batteries”
Antenna
A metal structure that radiates or receives electromagnetic waves, used in both radio transmitters and receivers. — see “Radio and the Birth of Wireless Communication”
Antibiotic
A medicine that kills or inhibits the growth of bacteria, used to treat bacterial infections. — see “The Discovery of Penicillin and the Antibiotic Era”
Antibiotic resistance
The ability of bacteria to survive exposure to an antibiotic that would normally kill them, often through genetic changes or protective enzymes. — see “The Discovery of Penicillin and the Antibiotic Era”
Arc lighting
A form of electric lighting produced by a continuous electrical discharge jumping across a gap between two electrodes. — see “The Electric Light and the Development of Practical Lighting”
ARPANET
The U.S. government-funded packet-switched network, first connected in 1969, that became the internet's direct predecessor. — see “The Origins and Expansion of the Internet”
Atmospheric engine
An early steam engine design, such as Newcomen's, that used atmospheric pressure to push a piston into a steam-created vacuum. — see “The Steam Engine and the Mechanization of Work”
Atomic clock
An extremely precise timekeeping device that measures time based on the vibrations of atoms, essential to GPS accuracy. — see “GPS and Satellite Navigation”
Attenuation
The reduction in strength of radiation as it passes through a material, which varies with the material's density. — see “X-Rays and the Ability to See Inside Matter”

B

Barcode
A machine-readable pattern of parallel bars and spaces that encodes identifying information. — see “The Barcode and the Automation of Product Identification”
Base pairing
The chemical rule by which DNA's bases bond in specific pairs, adenine with thymine and guanine with cytosine, across the two strands of the helix. — see “The Discovery of the Structure of DNA”
Beta-lactam
A chemical ring structure found in penicillin and related antibiotics that disrupts bacterial cell wall formation. — see “The Discovery of Penicillin and the Antibiotic Era”
Binary code
A system of representing information using only two values, typically 0 and 1, used internally by electronic computers. — see “From Mechanical Calculators to Electronic Computers”
Boiler
A vessel in which water is heated to produce pressurized steam for driving an engine. — see “The Steam Engine and the Mechanization of Work”
Browser
Software that requests, displays, and allows navigation of web pages and other resources on the World Wide Web. — see “The World Wide Web and the Organization of Online Information”

C

Calotype
William Henry Fox Talbot's negative-based photographic process, which allowed multiple positive prints to be made from one paper negative. — see “Photography: From Chemical Plates to Permanent Images”
Camera obscura
A darkened box or room with a small opening that projects an inverted image of an external scene onto an interior surface. — see “Photography: From Chemical Plates to Permanent Images”
Carburetor
A device that mixes air and fuel in the correct proportion before it enters an engine's cylinders. — see “The Internal Combustion Engine”
Cathode
The electrode in a battery that accepts electrons during discharge; in a lithium-ion cell, typically a lithium metal oxide. — see “The Development of Lithium-Ion Batteries”
Cathode ray tube
A sealed glass tube from which most air has been removed, inside which a beam of electrons travels between electrodes under high voltage. — see “X-Rays and the Ability to See Inside Matter”
Cell
The basic structural unit of living organisms, first named by Robert Hooke after viewing cork tissue under a microscope. — see “The Microscope and the Discovery of the Invisible World”
Cellulose fiber
The plant-based structural fiber that, once pulped and re-felted, bonds together to form a sheet of paper. — see “The Development of Paper and Written Information”
Chariot
A fast, light, wheeled vehicle, typically horse-drawn, used in ancient warfare, ceremony, and racing. — see “The Wheel: Origins, Uses, and Historical Impact”
Chromatic aberration
An optical distortion in which a lens focuses different colors of light at slightly different points, causing blurring or color fringing. — see “The Telescope and the New View of the Universe”
Chromosome
A structure within a cell's nucleus that contains tightly packaged DNA carrying an organism's genetic information. — see “The Discovery of the Structure of DNA”
Circuit
A closed loop of wire through which electric current can flow, completed or broken to send a signal. — see “The Telegraph and Long-Distance Communication”
Cladding
The outer layer of an optical fiber surrounding the core, with a lower refractive index that keeps light confined inside the core. — see “Fiber Optics and Communication Through Light”
Coherer
An early radio wave detector consisting of loose metal filings that clumped together when struck by a radio signal. — see “Radio and the Birth of Wireless Communication”
Compositor
A printing worker responsible for arranging individual pieces of type into words, lines, and pages before printing. — see “The Printing Press and the Expansion of Knowledge”
Compound microscope
A microscope using two or more lenses in sequence, typically an objective lens and an eyepiece, to achieve magnification. — see “The Microscope and the Discovery of the Invisible World”
Compression ignition
An engine design, used in diesel engines, that ignites fuel through the heat of highly compressed air rather than a spark. — see “The Internal Combustion Engine”
Condenser
A chamber where steam is cooled and turned back into water, used in Watt's engine to avoid cooling the main cylinder. — see “The Steam Engine and the Mechanization of Work”
Crank
A mechanical linkage that converts the back-and-forth motion of a piston into rotary motion. — see “The Steam Engine and the Mechanization of Work”
Crankshaft
A rotating shaft that converts the up-and-down motion of an engine's pistons into rotary motion. — see “The Internal Combustion Engine”

D

Daguerreotype
An early photographic process using a silver-coated copper plate, producing a single, unique, highly detailed image. — see “Photography: From Chemical Plates to Permanent Images”
Dead reckoning
A navigation method that estimates current position using a known starting point, speed, heading, and elapsed time, without external positional fixes. — see “The Magnetic Compass and the Transformation of Navigation”
Direct current (DC)
Electric current that flows steadily in one direction, used in Edison's original lighting systems. — see “The Electric Light and the Development of Practical Lighting”
Doping
The process of adding small amounts of other elements to a semiconductor crystal to control how it conducts electricity. — see “The Transistor and the Miniaturization of Electronics”
Double helix
The twisted, ladder-like shape formed by two strands of DNA wound around each other. — see “The Discovery of the Structure of DNA”
Drag
The resistance a moving aircraft encounters from the air it passes through. — see “The Airplane and the Development of Controlled Flight”

E

Electrodynamics
The branch of physics describing the forces and interactions between electric currents, formalized by André-Marie Ampère. — see “The Discovery of Electromagnetism”
Electrolyte
The medium between a battery's electrodes that allows ions, but not electrons, to pass through it. — see “The Development of Lithium-Ion Batteries”
Electromagnet
A magnet created by running electric current through a coil of wire, producing a magnetic field only while current flows. — see “The Discovery of Electromagnetism”
Electromagnetic induction
The generation of an electric current in a conductor caused by a changing magnetic field near it, discovered by Faraday in 1831. — see “The Discovery of Electromagnetism”
Electromagnetic radiation
Energy that travels through space as waves, including visible light, radio waves, and X-rays, distinguished by wavelength. — see “X-Rays and the Ability to See Inside Matter”
Electromagnetic wave
A wave of oscillating electric and magnetic fields that travels through space at the speed of light, the physical basis of radio. — see “Radio and the Birth of Wireless Communication”
Electromechanical
Describing a device, such as an early calculator, that performs its function using electrically controlled mechanical parts like relays. — see “From Mechanical Calculators to Electronic Computers”
Energy conversion efficiency
The percentage of incoming sunlight a solar cell actually converts into usable electricity. — see “The Development of the Modern Solar Cell”
Energy density
The amount of energy a battery can store relative to its weight or volume. — see “The Development of Lithium-Ion Batteries”

F

Fermentation
A biological process in which microorganisms, such as mold or yeast, are grown in bulk to produce a useful substance, as was done to mass-produce penicillin. — see “The Discovery of Penicillin and the Antibiotic Era”
Filament
The thin wire or thread inside a lamp that heats up and emits light when electric current passes through it. — see “The Electric Light and the Development of Practical Lighting”
Fixing
The chemical step that stops a photographic image from continuing to darken or fade after exposure and development. — see “Photography: From Chemical Plates to Permanent Images”
Fluorescence
The emission of visible light by certain materials when they absorb radiation, such as X-rays, that is otherwise invisible. — see “X-Rays and the Ability to See Inside Matter”
Forme
The locked frame of assembled type used to print a page in a traditional letterpress printing process. — see “The Printing Press and the Expansion of Knowledge”
Four-stroke cycle
An engine operating cycle consisting of intake, compression, power, and exhaust strokes. — see “The Internal Combustion Engine”
Fused deposition modeling
An additive manufacturing process that builds objects by extruding melted thermoplastic filament through a nozzle, layer by layer. — see “The Development of 3D Printing”

G

Geomancy
A traditional practice of using earth-related signs, including magnetic orientation, to guide decisions about site selection and design. — see “The Magnetic Compass and the Transformation of Navigation”
Geostationary orbit
A high orbit about 35,786 kilometers above the equator where a satellite's period matches Earth's rotation, so it appears stationary from the ground. — see “Artificial Satellites and Space-Based Technology”

H

Heliocentrism
The astronomical model holding that the Sun, rather than Earth, is at the center of the solar system. — see “The Telescope and the New View of the Universe”
HTML
Hypertext Markup Language, the system used to structure and format documents for display on the World Wide Web. — see “The World Wide Web and the Organization of Online Information”
HTTP
Hypertext Transfer Protocol, the set of rules governing how web browsers and servers request and exchange data. — see “The World Wide Web and the Organization of Online Information”
Hypertext
Text displayed on a computer that contains links to other documents or resources, allowing nonlinear navigation between them. — see “The World Wide Web and the Organization of Online Information”

I

Incandescent lamp
A light source that produces light by heating a filament with electric current until it glows. — see “The Electric Light and the Development of Practical Lighting”
Integrated circuit
An electronic circuit with multiple components built together on a single piece of semiconductor material, commonly called a chip. — see “The Integrated Circuit and the Growth of Modern Computing”
Intercalation
A chemical process in which ions, such as lithium, insert themselves reversibly into the layered structure of another material without permanently altering it. — see “The Development of Lithium-Ion Batteries”
Internal combustion
An engine design in which fuel is burned directly inside a cylinder to produce power, rather than externally as in a steam engine. — see “The Internal Combustion Engine”

L

Launch vehicle
The rocket used to carry a satellite from Earth's surface into orbit. — see “Artificial Satellites and Space-Based Technology”
Lift
The upward force generated as air flows over a wing's curved surface, counteracting an aircraft's weight. — see “The Airplane and the Development of Controlled Flight”
Lodestone
A naturally occurring magnetized piece of the mineral magnetite, capable of attracting iron and aligning with Earth's magnetic field. — see “The Magnetic Compass and the Transformation of Navigation”
Low Earth orbit (LEO)
An orbital band a few hundred to about two thousand kilometers above Earth, used by many satellites and the International Space Station. — see “Artificial Satellites and Space-Based Technology”

M

Magnetic declination
The angular difference between magnetic north, as shown by a compass, and true geographic north at a given location. — see “The Magnetic Compass and the Transformation of Navigation”
Magnetic field
A region of space around a magnet or current-carrying wire in which magnetic forces can be detected. — see “The Discovery of Electromagnetism”
Magnification
The degree to which an optical instrument enlarges the apparent size of an object being viewed. — see “The Microscope and the Discovery of the Invisible World”
Mariner's compass
A compass mounted on a card marked with directional points, often gimbaled, used as standard navigational equipment aboard ships. — see “The Magnetic Compass and the Transformation of Navigation”
Medium Earth orbit (MEO)
The orbital band, roughly 20,000 kilometers above Earth, used by GPS and similar navigation satellites. — see “GPS and Satellite Navigation”
Modulation
The technique of varying a radio wave's amplitude or frequency to encode sound or other information onto it. — see “Radio and the Birth of Wireless Communication”
Moore's Law
The observation, made by Gordon Moore in 1965, that the number of transistors fitting on a chip tends to roughly double every couple of years. — see “The Integrated Circuit and the Growth of Modern Computing”
Morse code
A system of short and long signals (dots and dashes) representing letters and numbers, developed by Samuel Morse and Alfred Vail. — see “The Telegraph and Long-Distance Communication”
Movable type
Individual, reusable pieces of type, each representing a letter or character, that can be arranged and rearranged to print different texts. — see “The Printing Press and the Expansion of Knowledge”

N

Negative-positive process
A photographic method in which an initial negative image is used to produce any number of positive prints. — see “Photography: From Chemical Plates to Permanent Images”
NSFNET
A high-capacity academic network built by the National Science Foundation in the 1980s that greatly expanded internet access. — see “The Origins and Expansion of the Internet”
Nucleotide
The basic chemical building block of DNA, consisting of a sugar, a phosphate group, and one of four nitrogen-containing bases. — see “The Discovery of the Structure of DNA”

O

Objective lens
The primary light-gathering lens at the front of a refracting telescope or microscope. — see “The Telescope and the New View of the Universe”
Orbit
The curved path an object follows around a planet due to the balance between gravity and its forward motion. — see “Artificial Satellites and Space-Based Technology”

P

p-n junction
The boundary between two regions of a semiconductor doped with different impurities, where an internal electric field forms. — see “The Development of the Modern Solar Cell”
Packet switching
A method of data transmission in which information is broken into small units, or packets, that travel independently across a network. — see “The Origins and Expansion of the Internet”
Papermaking
The craft of turning plant or rag fiber into pulp and forming it into dried sheets for writing. — see “The Development of Paper and Written Information”
Papyrus
An ancient Egyptian writing material made from layered strips of the papyrus plant's pith, distinct from true paper. — see “The Development of Paper and Written Information”
Parchment
A writing surface made from treated animal skin, prized for durability but costly to produce. — see “The Development of Paper and Written Information”
Patent
A legal protection granting an inventor exclusive rights to an invention for a set period. — see “The Barcode and the Automation of Product Identification”
Patent caveat
A nineteenth-century legal filing that gave an inventor a preliminary, renewable notice of priority for an invention still in development, short of a full patent. — see “The Telephone and the Evolution of Voice Communication”
Payload
The instruments or equipment a satellite or rocket carries to perform its mission. — see “Artificial Satellites and Space-Based Technology”
Photodetector
A device that converts received light signals back into electrical signals. — see “Fiber Optics and Communication Through Light”
Photolithography
A manufacturing process that uses light projected through patterned masks to etch tiny circuit features onto a semiconductor wafer. — see “The Integrated Circuit and the Growth of Modern Computing”
Photon
A particle of light that carries energy; absorbing photons can free electrons in a solar cell's material. — see “The Development of the Modern Solar Cell”
Photopolymer
A liquid or soft material that hardens, or cures, when exposed to light, typically ultraviolet light. — see “The Development of 3D Printing”
Photovoltaic effect
The generation of electric voltage or current in a material when it is exposed to light. — see “The Development of the Modern Solar Cell”
Piston
A moving disk or cylinder inside an engine cylinder that is pushed back and forth to produce mechanical motion. — see “The Steam Engine and the Mechanization of Work”
Planar process
A manufacturing technique, developed at Fairchild Semiconductor, for building transistors and their connections on a flat silicon surface. — see “The Integrated Circuit and the Growth of Modern Computing”
Point of sale (POS)
The computer system at a checkout counter that processes sales, often by reading barcodes and retrieving pricing data. — see “The Barcode and the Automation of Product Identification”
Protocol
A set of agreed-upon technical rules that allow different computers and networks to exchange data reliably. — see “The Origins and Expansion of the Internet”
Pulp
A wet mixture of separated plant or rag fibers used as the raw material for papermaking. — see “The Development of Paper and Written Information”

R

Radiograph
An image produced by X-rays passing through an object and being recorded on a photographic plate or electronic detector. — see “X-Rays and the Ability to See Inside Matter”
Receiver
The part of a telephone that converts an incoming electrical signal back into sound by vibrating a diaphragm. — see “The Telephone and the Evolution of Voice Communication”
Reflecting telescope
A telescope that uses a curved mirror instead of a lens to gather and focus light, avoiding chromatic aberration. — see “The Telescope and the New View of the Universe”
Refracting telescope
A telescope that uses lenses to gather and focus light. — see “The Telescope and the New View of the Universe”
Refractive index
A measure of how much a material bends light passing through it, relative to light traveling in a vacuum. — see “Fiber Optics and Communication Through Light”
Relay
An electrically operated mechanical switch used in early calculating machines and computers before the adoption of electronic switching. — see “From Mechanical Calculators to Electronic Computers”
Relay station
An intermediate station that boosts or retransmits a signal to extend its range over long telegraph lines. — see “The Telegraph and Long-Distance Communication”
Resolution
The ability of an optical instrument to distinguish fine detail as separate, rather than blurred together. — see “The Microscope and the Discovery of the Invisible World”
Rolling friction
The resistance encountered when a round object rolls over a surface, generally much lower than the friction of dragging an object. — see “The Wheel: Origins, Uses, and Historical Impact”
Router
A device that directs data packets toward their destination across a network. — see “The Origins and Expansion of the Internet”

S

Satellite constellation
A coordinated group of satellites working together, such as the network of GPS satellites that together provide global coverage. — see “GPS and Satellite Navigation”
Selective Availability
A policy under which the U.S. military deliberately degraded civilian GPS signal accuracy until it was discontinued in 2000. — see “GPS and Satellite Navigation”
Selective laser sintering
An additive manufacturing process that uses a laser to fuse particles of powdered material, such as plastic or metal, into a solid shape. — see “The Development of 3D Printing”
Semiconductor
A material, such as silicon or germanium, whose electrical conductivity can be precisely controlled, making it useful for building electronic components. — see “The Transistor and the Miniaturization of Electronics”
Semiconductor wafer
A thin slice of silicon or another semiconductor material used as the base on which integrated circuits are manufactured. — see “The Integrated Circuit and the Growth of Modern Computing”
Sepsis
A life-threatening bodily response to infection that was a leading cause of death before effective antibiotics existed. — see “The Discovery of Penicillin and the Antibiotic Era”
Simple machine
A basic mechanical device, such as a lever, pulley, or wheel-and-axle, that changes the direction or magnitude of a force. — see “The Wheel: Origins, Uses, and Historical Impact”
Simple microscope
A microscope that uses a single lens to magnify a specimen, such as the instruments Antonie van Leeuwenhoek built. — see “The Microscope and the Discovery of the Invisible World”
Solid-state device
An electronic component, like a transistor, that controls current entirely within solid materials rather than through a vacuum or moving parts. — see “The Transistor and the Miniaturization of Electronics”
Space Race
The Cold War-era competition between the United States and the Soviet Union to achieve milestones in spaceflight. — see “Artificial Satellites and Space-Based Technology”
Spoked wheel
A lighter wheel design using thin rods, or spokes, connecting a central hub to an outer rim, reducing weight compared with a solid disk. — see “The Wheel: Origins, Uses, and Historical Impact”
Stereolithography
An additive manufacturing process that uses an ultraviolet laser to selectively harden successive layers of liquid photopolymer resin into a solid object. — see “The Development of 3D Printing”
Stored-program architecture
A computer design in which instructions are held in the same memory as data, allowing a computer's task to be changed without physically rewiring it. — see “From Mechanical Calculators to Electronic Computers”
Symbology
The specific set of rules defining how a barcode's bars and spaces represent encoded data. — see “The Barcode and the Automation of Product Identification”

T

TCP/IP
The combined set of protocols, developed by Vint Cerf and Robert Kahn, that governs how data is transmitted and addressed across interconnected networks. — see “The Origins and Expansion of the Internet”
Telegraph key
A manual switch used by a telegraph operator to open and close an electrical circuit, producing coded pulses. — see “The Telegraph and Long-Distance Communication”
Telephone exchange
A central facility, originally staffed by human operators, where telephone lines were manually connected to complete calls between subscribers. — see “The Telephone and the Evolution of Voice Communication”
Thermal runaway
A failure mode in which internal heating in a battery becomes self-sustaining, potentially leading to fire. — see “The Development of Lithium-Ion Batteries”
Three-axis control
A flight control system that manages an aircraft's roll, pitch, and yaw, pioneered by the Wright brothers. — see “The Airplane and the Development of Controlled Flight”
Total internal reflection
The complete reflection of light at the boundary between two materials when it strikes at a sufficiently shallow angle, keeping the light trapped inside the denser material. — see “Fiber Optics and Communication Through Light”
Transmitter
The part of a telephone that converts sound vibrations from a speaker's voice into a varying electrical signal. — see “The Telephone and the Evolution of Voice Communication”
Trilateration
A method of determining a precise location by measuring distances from multiple known reference points, such as satellites. — see “GPS and Satellite Navigation”
Type alloy
A metal mixture, typically including lead, tin, and antimony, used to cast durable, precisely sized printing type. — see “The Printing Press and the Expansion of Knowledge”

U

UPC (Universal Product Code)
The standardized rectangular barcode symbol adopted by the U.S. grocery industry in 1973 to identify products. — see “The Barcode and the Automation of Product Identification”
URL
Uniform Resource Locator, the unique address used to identify and locate a specific resource on the Web. — see “The World Wide Web and the Organization of Online Information”

V

Vacuum bulb
A sealed glass enclosure with air removed, used to protect a hot filament from burning up in contact with oxygen. — see “The Electric Light and the Development of Practical Lighting”
Vacuum tube
An older electronic component that used a heated filament inside a sealed glass tube to amplify or switch electrical signals. — see “The Transistor and the Miniaturization of Electronics”
Voltaic pile
The first chemical battery, invented by Alessandro Volta in 1800, which provided a steady electric current for experimentation. — see “The Discovery of Electromagnetism”

W

Wheel-and-axle
A simple machine consisting of a circular wheel attached to a central shaft, used to reduce friction or to multiply force. — see “The Wheel: Origins, Uses, and Historical Impact”
Wing warping
An early flight-control method, used by the Wright brothers, that twisted the wingtips in opposite directions to control roll. — see “The Airplane and the Development of Controlled Flight”
Wireless telegraphy
The transmission of coded messages, typically in Morse code, through electromagnetic waves rather than along a wire. — see “Radio and the Birth of Wireless Communication”
Woodblock printing
A printing method in which an entire page of text or image is carved into a single wooden block, inked, and pressed onto paper. — see “The Printing Press and the Expansion of Knowledge”

X

X-ray diffraction
A technique that reveals the structure of a molecule by analyzing the pattern X-rays form after passing through a crystallized or fibrous sample. — see “The Discovery of the Structure of DNA”