A – Z of Science Fiction words

A useful guide to scientific words for the Science Fiction enthusiast. It first appeared as monthly instalments in Authentic Science Fiction and was printed and published as a booklet by Hamilton & co., in the Goldhawk Road, London W 12. It was compiled by H.J. Campbell. Being 1954 very little is related to computers. At C you will find Cybernetics and at B Betelgeuse...

Absolute. Not relative. Independent of all scale and comparisons. E.g., zero temperature, number, the speed of light.

Acceleration. Rate of change of velocity. Increasing velocity is positive acceleration; decreasing velocity is negative acceleration. The average acceleration of any body falling to Earth in a vacuum is 32 feet per second per second.

Achromatic. Applied to optical apparatus which gives images free from colored fringes. A. lenses have one sense of crown glass and one of flint glass. The flint lens corrects dispersion caused by the crown glass.

Aerolite. (Sometimes called ‘aerolith’). A stony meteorite, as distinct from a metallic one. A meteorite that is a mixture of stone and metal, but preponderantly stone would be called aerolithic.

Albedo. A measure of the brightness of celestial bodies that shine by reflected light. Technically, it is the amount of light a body reflects in proportion to the amount that falls on it. The Moon’s albedo is 7%; that of Venus 65%.

Aldebaran. A star of the first magnitude in the constellation of Taurus. The brightest star near the Pleiades. It is much used in navigation.

Alpha rays. Streams of high-velocity Helium nuclei, composed of two protons (alpha particles) emitted from radioactive elements. A. rays produce ionisation in gases they pass through, and are easily absorbed by solid matter.

Angstrom unit. A distance of ten to the minus ten of a metre. One ten thousandth of a micron. It is the unit of distance most used as a measurement of electromagnetic wavelengths. Named after the Swedish physicist A. J. Angstrom.

Aphelion. The point on the Earth’s orbit where it is at greatest distance from the Sun. There are two such positions, one at each end of an elipse. These positions correspond to summer winter. (From ‘ap’ meaning away, and ‘helios’ meaning Sun.)

Apogee. The point in the orbit of any celestial body at which it is farthest from Earth. The Sun is at apogee when the Earth is at aphelion. (From ‘goes’ meaning Earth.)

Archimedes’ principle. The weight of the water displaced by a body that is floated or immersed is numerically equal to the apparent loss of weight of the body.

Argon. An inert gas, present in the atmosphere to the extent of 0.8%. Used commercially for filling electric bulbs.

Artificial radioactivity. Radioactivity induced by the bombardment of normally stable substance with charged particles of high energy or with neutrons. Consists in the emission of beta and gamma rays.

Asteroids. A belt of minor planets circling the Sun between Mars and Jupiter. There are over 1,500 of them, but none is much larger than 300 miles in diameter. On October 30th, 1937, the asteroid Hermes came within 485,000 miles of Earth–closer than any celestial body except the Moon. Hermes is only one mile in diameter.

Astrocompass. Instrument that gives direction based on the positions of the stars and is independent of magnetism.

Athermancy. Opaqueness to radiant heat. A theoretical black body is completely athermant, i.e., absorbs all the radiant heat that falls upon it. A theoretical white body is completely non-athermant, i.e., reflects all the radiant heat that falls upon it. Other bodies show degrees of A.

Atmosphere. The gaseous layer above the surface of a celestial body. Earth’s atmosphere ceases to show significant resistance above about 500 miles. There is no sudden stop. The thinness gradually increases until no atoms are detectable in any reasonable sample. The pressure exerted by these miles of air at sea level is about 14.7 lbs. per sq. inch.

Atom. The smallest unit of matter that will take part in chemical reactions. Consists of a positively charged nucleus composed of protons and neutrons, and a variable number of orbital rings of electrons. It is the number of these electrons that determines the chemical properties of the atom.

Atomic bomb. An arrangement whereby a maximum number of nuclear fissions occur in minimum time by the very rapid collision of two subcritical masses of fissile material, the first fission setting off a chain reaction that is complete in a period of time of the order of one hundred thousandth of a second.

Atomic weight. The total weight of a neutral atom relative to the atomic weight of oxygen, which is taken as 16.00.

Aurora borealis. Coloured luminescent phenomena occuring in the polar regions as a result of solar radiation associated with sunspots.

Azimuth. The angle that the meridian and the vertical circle through a celestial body make with the zenith, measured as an arc on the horizon.

Band spectra. Whereas atoms give spectra consisting of a series of separate lines, molecules absorb or emit light to give band spectra. Examination of band spectra has given us a good deal of knowledge about sunspots and the cooler stars. Recently, certain band spectra in interstellar space were identified with molecules of carbon and hydrogen.

Betelgeuse. A supergiant red star in the constellation of Orion. Michelson in 1920 at Mt. Wilson, proved that this star is larger than Earth’s orbit. Yet its density is lower than that of fairly good vacuum.

Binary system. Two stars revolving around a common centre of gravity somewhere between them. 17,180 binaries have been listed. They furnish far more knowledge of stellar physics than any single star could do and are under very active observation–although over a hundred years must pass before the collection of certain relevant data can be completed.

Beta rays. Streams of fast-moving electrons and positrons, of much greater penetrating power than alpha rays. They are emitted by radioactive elements with velocities that sometimes exceed 98% of the velocity of light.

Betatron. An apparatus for speeding up electrons to very high energy values. A varying magnetic field, perpendicular to the electrons’ circular orbits, furnishes the accelerating force in a high vacuum.

Binomial. A mathematical expression is binomial when it is concerned with the difference or the sum of two terms

Bivalent. The property of having two chemical bonds available for reactions. A bivalent atom could unite with two monovalent atoms or one divalent atom.

Black body radiation. Radiation emitted by an ideal black body, which absorbs all incident radiations and thus radiates itself only as an expression of its temperature.

Boyle’ Law. The volume of a given amount of gas is inversely proportional to the pressure, at constant temperature.

Brownian movement. Patternless vibrations of small particles cause by the bombardment of molecules composing the medium.

Catalyst. A substance which alters the rate of a chemical reaction without itself undergoing any change. Our digestive juices are catalysts produced by living cells.

Celestial equator. The circle which the plane of the Earth’s equator makes on meeting the Celestial Sphere.

Celestial Sphere. An imaginary sphere on which the heavenly bodies are supposed to lie. We stand at its centre.

Cepheid variables. Stars that fluctuate in brightness over a given period. The longer the period, the brighter the star. These variables enable astronomers to measure very great distances.

Chromosphere. Layer outside the photosphere of the Sun. The chromosphere is normally only visible at total eclipse.

Cloud chamber. An instrument used for the study of alpha, beta, gamma and x-rays, in which the rays are passed through a vessel supersaturated with water vapour, leaving tracks of water droplets caused by ionisation.

Clusters. Groups of stars. Open clusters, like the Pleiades, consist of 500 stars over a wide area. Globular clusters, like NGC6553, are composed of thousands of stars in a compact mass lying outside the Milky Way.

Ceolostat. An instrument consisting of a mirror mounted so that it turns on an axis parallel to the Earth’s. Clockwork drives it westwards as the Earth turns eastwards; it reflects a constant image into a stationary telescope.

Colour. Imaginary property caused by the effect of electromagnetic waves on the retina. Each colour of of the spectrum has its own wave length.

Comet. A hazy cloud of gas with a bright nucleus and a faint tail, moving under the Sun’s attraction in a highly eccentric orbit.

Commutator. Instrument for reversing the direction of an electric current.

Complementary colours. Colours which in combination produce white.

Condensation. The phenomen of the return to the liquid state of a substance that has become vaporized.

Condenser. Optical: any arrangement for bringing a beam of light to a point. Chemical: Apparatus for effecting condensation. Electrical: an arrangement for storing electricity in the static form.

Conic sections. Figures resulting from cutting a cone at various levels and in various planes.

Conjunction. Any body in line with the Sun and the Earth is in conjunction. On the near side it is the inferior conjunction; on the far side it is the superior conjunction. In the opposite direction to the Sun, it is in opposition.

Conservation of energy and mass. A principle resulting from the theory of relativity which states that the total mass and energy times the velocity of light is constant for any coordinate system. Simply, it means that matter and energy are interconvertible and cannot be either created or destroyed. Although this holds for all terrestrial phenomena, recent theories of cosmogony assume that matter is being continuously created in interstellar space from nothing. Both are mathematical concepts rather than physical ones, and only the most expert mathematicians really understand them.

Continuum. An intermingling series of continuous components. Three space dimensions and the time dimension are continuous components intermingling to form the four dimensional continuum of the everyday world.

Corona. The Sun’s incandescant halo that is only visible during total eclipses.

Cosmic dust. Tiny particles of matter up to a hundredth of a millimeter in diameter that are present throughout the whole of space.

Cosmic rays. Energetic charged particles colliding with Earth from outer space. Mostly protons, but also some electrons and a few heavy atomic nuclei–up to the atomic weight of iron.

Cosmic static. Long wave radio emissions coming from extended regions of the Milky Way. Not observable beyond 30 degrees either side of the Milky Way, and most intense in Sagittarius.

Cosmogony. Theoretical explanation of the origin of celestial bodies individually collectively.

Crab nebula. Exploding remains of a supernova that was observed by Chinese astronomers in A.D. 1054. Still exploding at the rate of many hundreds of miles a second. The star it came from had a luminosity equivalent to 30 millions of our Sun!

Critical mass. The minimum mass of fissionable material that can undergo a self-sustained chain reaction of nuclear fissions, such that the total fissions occur within a very short time. One of the most closely guarded of atomic secrets. The atomic bomb contains two pieces of fissionable material that are hurled together to make critical mass at the moment of explosion.

Curie. Unit of radioactivity that is equivalent to the amount of a radioactive substance that decays at the rate of 3.7X1010 per second.

Cybernetics. The study of communication and control mechanism in machines and living things. The science of the relationships between the central control, the peripheral effectors and the communication channels between.

Cyclotron. Instrument for accelerating electrons or other charged particles by dragging them magnetically between two hollow semi-circular electrodes.

Dark nebula. Obscuring clouds in the Milky Way consisting of myriads of cosmic dust particles.

Deimos. Mars’ smallest moon; five miles in diameter.

Deliquescent. The property of picking up water from the environment and dissolving in it. A deliquescent substance becomes a liquid when exposed  to ordinary air.

Delta rays. Low speed electrons that have been emitted by a substance under bombardment of alpha rays.

Desiccation. The process of drying; removal of water.

Deuterium. Isotope of hydrogen obtained by fractional electrolysis of water. In combination with oxygen gives heavy water.

Dialysis. Phenomenon of selective diffusion of colloids through a semi-permeable membrane.

Diathermancy. Transparency to heat.

Diatomic. Molecule composed of two atoms of the same kind.

Dielectric. Synonym for a non-conductor.

Diffuse nebulae. Formless masses of clouded luminosity, as seen in Orion, for example.

Digit. One twelfth of the diameter of the Sun or Moon. Used in measuring the extent of eclipses.

Diode. Thermionic valve containing two electrodes in the form of anode and cathode.

Deport. Unit of lentiform power, in which the reciprocal of the focal length of a lens in metres is expressed as so many deportees.

Dispersion. Resolution of mixed light into separate wave bands, as in a spectroscope.

Diurnal. An action or process occurring every twenty-four hours. Man, and other animals that sleep at night, are said to have a diurnal rhythm. Diurnality on other planets need not be correlated with twenty-four hours; it is the length of day that matters.

Doppler effect. The frequency of any wave phenomenon appears greater to an observer moving away. This principle has been extended to the nebulae, which appear to give off a redder (i.e. lower frequency) light than they would if they maintained the same position relative to Earth. Such observations indicate that the nebulae are all receding from Earth (and its Galaxy).

Ductility. A metal is said to be perfectly ductile when it is capable of being drawn out to great length.

Duralumin. A hard aluminium containing 4 per cent copper and traces of manganese, magnesium and silicon.

Dwarf star. Main sequence stars of absolute magnitude greater than 1. Stars of low luminosity.

Dynamite. Nitroglycerine absorbed in Kieselguhr. Kieselguhr is an inactive earth consisting of the siliceous skeletal remains of diatoms.

Dyne. The absolute unit of force. A dyne, acting on a mass of one gram will give it an acceleration of one centimetre per second per second.

Eclipse. Obstruction of the light from a luminous body by another celestial body between it and the observer or between the luminous body and its illuminant.

Ecliptic. The apparent path of the Sun on the celestial sphere, i.e. relative to the stars.

Electrode. An electric terminal used to transfer an electric charge through a surrounding medium to another electrode. Positive electrodes are anodes; negative electrodes are cathodes.

Electrolysis. The chemical splitting of a medium into components by the passage of an electric current.

Electromagnetic waves. Waves that do not require a medium for their passage, and which travel at the speed of light (which is one form of electromagnetic wave; other forms are infrared, ultraviolet, x-rays, wireless waves, gamma rays, etc.).

Electron. A subatomic particle of negative charge, with a mass of 9.107X10-28 and a charge of 4.803X10-10 electrostatic units. Electrons form spheres of negative charge surrounding the positively charged atomic nucleus.

Electron microscope. Device for the high magnification of a very thin object in vacuo by means of a beam of electrons in place of visible light.

Electrostatic unit of electricity. The amount of electricity that repels a similar amount with a force of one dyne when placed one centimeter from it in a vacuum.

Element. A substance composed of one kind of atom only.

Emission spectrum. Spectrum obtained by examination of light coming from an actual source (i.e., not reflected light).

Endothermic. A reaction is endothermic when heat is absorbed in the course of it.

Energy. Capability of doing work. The particular form that energy takes depends on the characteristics of the system in which it is produced.

Entropy. A measure of the degree of molecular disorder of a system, based on the ratio of the amount of heat absorbed to the absolute temperature at which it is absorbed. Entropy cannot decrease but must either remain constant for any particular system or must increase. Since all reactions in the universe are fundamentally irreversible, total universal entropy is increasing. In other words, the universe is becoming more and more disorderly!

Equilibrium. A state in which opposing forces are exactly balanced.

Equinox. Point at which the Sun’s apparent path (ecliptic) intersects the celestial equator.

Erg. Physical unit of work; done by one dyne acting over a distance of one centimeter.

Faculae. Bright spots or ‘torches’ near the edge of the Sun.

Fahrenheit degree. 1/180th of the difference between the temperature of melting ice and the boiling point of water under standard pressure (760mm, Hg.).

Falling star. Erroneous name for the luminescent phenomena associated with a meteorite.

Fission. The breakdown of atomic constituents into a lighted atom and radioactive products.

Fitzgerald contraction. The contraction in length in the direction of motion experienced by a body moving at very high velocities. The theory was put forward by Fitzgerald in 1893, and was confirmed by the relativity theory (Einstein, 1905).

Fluorescence. The property of substances such as quinine sulphate to absorb light (or other electromagnetic radiation) of one colour (or wavelength) and to emit light of another colour (or wavelength) at the same time or later. An independent source of light is essential.

Fourth dimension. Now accepted and proved by the relativity theory to be time. A material object cannot be properly described without mention of its time position. Non-materially, mathematical equations can describe relations in any number of hypothetical dimensions. Such dimensions are known technically as hyperspace.

Frequency. The number of vibrations per second of a wave motion. Equal to the velocity divided by the wavelength.

Friction. Force opposing the free movement of surfaces in relative motion.

Galaxy. A gigantic cluster of stars and, some think, planets. The Earth and the Solar System form a comparatively minute speck in the galaxy of the Milky Way. The nearest galaxy to our own lies in Andromeda and is 750,000 light years away. It is just visible to the naked eye. The most distant galaxy observable with the 200” telescope at Mt. Palomar is about 100 million light years away. Galaxies are sometimes called nebulae and are of several different types.

Gamma rays. Very short electromagnetic waves usually produced by radioactive disintegration.

Geiger counter. An instrument consisting of a coaxial cylindrical metallic cathode surrounding a wire anode. The electrodes are enclosed in an evacuated glass vessel. An incoming ionized particle produces ions inside the vessel which are accelerated towards their equivalent electrodes by the applied potential difference (about 1,000 volts). A drop in potential is thus caused, and this can be made to trigger electronic circuits which automatically count, and/or actuate a sonal device.

Geodesic. Minimum distance between two points on a sphere. As applied on Earth, geodesic means ‘as the crow flies.’

Gravity. The force with which every particle of matter in the universe attracts every other particle. It is inversely proportional to the square of the  distance between the particles and directly proportional to the product of their masses.

Ground state. An atomic state at which the electrons move at minimum energy levels. Sate of maximum stability.

Half-life. Time required for the radioactive decay of one half of any mass of a radioactive element.

Harvest Moon. The Moon, in September, rises almost at the same time each evening, so that the nights are well-lit at harvest time.

Heat. The energy represented by a substance’s molecular movement. Increase in movement is increase in heat and vice versa. Temperature is a measurement of this in degree of molecular movement.

Heaviside layer. The ionosphere. A band in the upper atmosphere from 38 to 185 miles above sea-level. Consists mainly of ionized particles, which reflect radio waves and make world-wide radio communication possible.

Heavy water. Water in which the hydrogen is the heavy isotope iH2.

Helium. An inert, rare gas, one part of which occurs in 200,000 parts of our atmosphere. Helium is peculiar in that at temperatures near absolute zero, it appears to behave independently of gravity–climbing the sides of its container and falling over the rim.

Heterodyne. The superimposition of two waves of different frequencies to produce a heat effect. A means of changing the frequency of an alternating current.

Homologues. Developmental equivalents. The Eustachian tube, for example, is homologous with the first gill cleft in fishes, having been derived from it by evolution.

Hormones. Endocrine gland (thyroid, adrenal, etc.) productions that play an important part in regulating bodily functions such as growth. Essential to health, sometimes to life.

Hydrogen. Lightest substance known. A gas the diatoms of which consist of one promote and one electron.

Hydroponics. Soil-less cultivation of plants. The roots are submerged in a solution containing only those nutriments required by the particular plant. In most cases superior to cultivation in soil.

Hygroscopic. Any substance that tends to absorb water from the air is hygroscopic. Examples: calcium chloride, lime, silica gel. May be used in spaceships to remove expired water from the atmosphere.

Hyperbola. A curve resulting when a cone is cut along a plane that makes a larger angle with the base than that made by the side of the cone. Path followed by a body projected from a planetary surface at a speed greater than escape velocity.

Ichthyosaur. A class of fossil reptiles which lived during the mesozoic era. Their form resembled that of fish and they lived in salt water.

Illumination. The amount of light, measured in lumens, falling in unit area in one second.

Immunity. The ability of an animal or plant to resist infection by parasites (e.g., viruses, bacteria, fungi).

Impulse. The product of the magnitude of a force and the time during which it acts.

Inert gases. The elements helium, neon, argon, krypton, xenon, and radon, which occur in minute amounts in the atmosphere are absolutely inactive chemically.

Inertia. The tendency of a mass to preserve motion in a straight line or to maintain a state of rest.

Infinity. An imaginary quantity that is greater than any assignable quantity.

Insolation. Exposure to solar radiation.

Interferometer. Instrument that divides a light beam and then reunites it to form an interference pattern. Used for measuring the diameters of stars. The one at Mt. Wilson can measure the angle that a pinhead in London would subtend at Carlisle.

Inverse square law. The law obeyed by gravity, light intensity, electric field discharge, etc. According to the law an effect caused by a source at x at a point y, varies inversely as the square of the distance xy.

Ion. An electrified atom. May be positve (few electrons) or negative (more electrons). The proton is a hydrogen ion.

Ionosphere. A layer of atmosphere composed largely of ions, that reflects radio waves.

Joule. Electrical unit of work, done by a current of one ampere flowing for one second through a resistance of one ohm.

Jupiter. Sol’s fifth planet, 483 million miles from the Sun. Has a year of 11.86 Earth years. Largest planet in the solar system.

Karyokinesis. Another name for mitosis, i.e., non-sexual cell division.

Kepler’s Laws. (1) The planets move about the Sun in eclipses, at one focus of which the Sun is located. (2) The radius vector joining each planet with the Sun describes equal areas in equal times. (3) The ratio of the square of a planet’s year to the cube of the planet’s mean distance from the Sun is the same for all planets.

Kinetic energy. The energy possessed by a body solely by virtue of its motion.

Lamarckism. The (obsolete) doctrine that acquired characters can be inherited.

Lambert. Unit of brightness, found when a perfectly diffusing surface emits or reflects one lumen per square centimetre.

Libration. Most often applied to the Moon. The oscillations which cause the edge of the disc to be alternately visible and invisible.

Lichen. Symbiotic association of an alga and a fungus to form one effective plant, which is able to live under extremely arduous conditions. In the colonisation of barren areas, lichens are the first plants to gain a foothold and prepare the soil for more complex vegetation. They probably represent the only form of life as we know it on Mars, and would play an important part in the colonisation of arid planets, being able to exist on bare rock and sand.

Light. Electromagnetic waves of length between 4X10-5cm. and 7X10-5cm. Velocity 186,326 miles per second is considered to be maximum velocity in the universe for any material particle.

Light pressure. The pressure exerted by sunlight on Earth’s surface is 2lbs. per square mile. It is thought that the light pressure on a comet’s tail is what causes it to point away from the Sun.

Light year. Distance travelled by light in one year. Six million million miles.

Magellanic clouds. Two star masses to one side of this galaxy and probably independent of it. They are at the zenith when seen from the Magellanic Straits.

Magnetism. The force of attraction or repulsion between magnetised bodies. The essential character of magnetism is thought to lie in the regular end-to-end arrangement of the molecular aggregates in the body. All large bodies, such as planets and stars, possess magnetism.

Magnetron. Instrument for generating radio waves in the centimetre range. Essential part of radar equipment.

Magnitude. Relative apparent brightness of a star. Each magnitude is 2.51 times as bright or dim as the next magnitude. First magnitude stars are brightest.

Mars. Sol’s fourth planet, 141.5 million miles from the Sun. Its year is 1.88 Earth years.

Meson. Cosmic particles of intermediate mass between the proton and electron. Several kinds of mesons are known.

Meteorite. A metallic body from outer space which becomes a shooting star on entering Earth’s atmosphere.

Moderator. A substance such as graphite or heavy water which is used in an atomic pile to slow down neutrons emitted as products of nuclear fission.

Momentum. Product of mass and velocity.

Nadir. Point on the celestial sphere opposite the zenith.

Nebulae. Either galaxies or the stuff that galaxies are made of. forming luminous or cloudy areas outside the Milky Way.

Neolithic. The new stone age–when agriculture began on Earth. About 10,000 years ago.

Nephascope. An instrument for timing the transit of celestial bodies and thereby determining their speed.

Neptune. Sol’s eighth planet, 2793.5 million miles from the Sun. Its year is 164.79 Earth years

Neutrino. A postulated subatomic particle with no charge and no (or very little) mass when at rest. Its postulation is necessary for the acceptance of the laws of conservation of energy/mass/momentum.

Neutron. Uncharged subatomic particles present in all atomic nuclei except that of hydrogen. Mass 1.00893 a.m.u. High penetrative power. Product of radioactive fission.

Newton’s Laws of Motion. (1) Every body continues in its state of rest or uniform motion in a straight line, except in so far as it is compelled by external forces to change that state. (2) The rate of change of momentum of a body is proportional to the external force, and takes place in the direction in which the force acts. (3) To every action there is an equal and opposite reaction.

Nova. Sudden contraction of a star, liberating an enormous amount of energy and giving rise to a brief increase in brightness. When the brightness dies down, there remains a white dwarf star.

Nuclear Charge. The electrical charge on the nucleus of an atom that exactly balances the opposite charge on the electrons in the shell. A decrease in the electronic charge gives a positive ion; an increase gives a negative ion. The nuclear charge is numerically equal to the number of electrons in the shell, to the number of protons in the nucleus and to the atomic number of the atom.

Nuclear fission. The splitting of an atom into two smaller atoms of nearly equal mass by breaking up of the original atom’s nucleus. May be accompanied by tremendous release of energy, or may be calm as in natural radioactive decay.

Nylon. A variety of synthetic polymeric amides. Normally the extrusion product of a condensed polymerisation of adipic acid and hexamethylene diamine.

Occultation. A heavenly body is occulted when another such body passes across its image. Eclipses are such.

Ohm. Unit of electrical resistance in which energy is used at the rate of one watt by the flow of one absolute ampere of current.

Ontogeny. Developmental (embryological) sequence of an organism.

Open Cluster. Collection of stars–such as the Pleiades–forming a fairly compact mass outside the Milky Way.

Opposition. A heavenly body, viewed from Earth, is in opposition when it lies in a direction opposite to that of the Sun. Antonym, conjunction.

Orbit. The path transcribed by an electron round a nucleus, or a planet round a star, or a satellite round a primary. Also means an eye-socket.

Parabola. Curve formed by making a cut through a cone parallel to the side of the cone. Every point on the curve is equidistant from a focus and a directrix.

Parallax. Change in apparent position of an object due to a change in the position of the observer.

Parsec. Distance represented by a parallax of one second of arc. 19X1012 miles, or 3.3 light years.

Pentode. A thermionic valve with anode, cathode and three grids, the control grid, screen grid and suppressor grid.

Perigee. The point on a planet’s orbit at which it is nearest Earth.

Perihelion. Point on a planet’s orbit at which it is nearest the Sun.

Perpetual motion. Object of perpetual search by pseudo-scientists looking for a machine that will work for ever without added energy.

pH. A measure of alkalinity and acidity expressed as a concentration of hydrogen ions.

Phone. Unit of loudness of sound.

Phot. A unit of illumination equal to one lumen per square centimetre.

Photocell. An apparatus for converting changes in incident light into electrical impulses.

Photon. A quantum of radiant energy.

Photosphere. The portion of the Sun’s disc that is visible to the eye.

Photosynthesis. The synthesis of carbohydrates by the polymerisation of formaldehyde, formed from carbon dioxide in plants due to a catalysis by chlorophyll under the influence of sunlight.

Pi. The mathematical symbol for the constant ratio between the diameter of a circle and its circumference. Numerically, 3.14.

Piezo-electric effect. The phenomenon of electrical charges appearing on opposite faces of an asymmetrical crystal due to pressure on the crystal due to pressure on the crystal.

Planck’s constant. 6.624X10-27 erg.sec. This constant, symbolized by h, gives the relation between the frequency of a radiation and its quantum of energy by the equation E=hv, where E is energy and v is frequency. The constant is of great importance in relativity and the geometry of space and time.

Planetoid. Synonymous with asteroid, a small celestial body orbiting the Sun, not a planet. It is possible that the asteroids are sometimes caught in the gravity fields of large planets; they then become satellites.

Planet. A celestial body orbiting a luminary (sun).

Plutonium. A man-made element two places higher than uranium in the periodic system. Produced during the nuclear bombardment of uranium, and itself undergoing explosive nuclear fission by slow neutrons. (At. No. 94.)

Q-value. Effective energy produced in a nuclear reaction expressed in terms of millions of electron volts.

Quantum. Amount of energy dependent upon the frequency of the radiation associated with electromagnetic waves by the relation Q=hv, where h is Planck’s constant and v is the frequency.

Radical. A group of atoms which retains its form throughout a chemical reaction.

Radioactivity. Emission of charged particles during the spontaneous decay of unstable atomic nuclei such as radium.

Radius vector. The line joining a planet with the centre of its orbital area.

Rectifier. An apparatus for the conversion of an alternating current to a direct current.

Relativity. The concept that absolute motion cannot be determined, and the corollaries that follow from this. It has two basic axioms: (a) that the velocity of light is constant for all observers, and (b) that natural laws operate in the same way for all observers, and (b) that natural laws operate in the same way for all observers. Most significant corollaries are: (a) the Fitzgerald-Lorentz contraction, (b) that the mass of a body increases with its velocity, and (c) that mass and energy are different aspects of the same thing. The special theory of relativity deals with the observable phenomena in two states in uniform motion relative to each other. The general theory of relativity concerns observable phenomena in systems not in uniform motion relative to each other.

Rest mass. The mass of a body when at rest, as opposed to its increasing mass with increasing velocity.

Resultant. The single force identical in effect with the effect of several co-acting forces.

Rocket. Device in which the motive power comes from the internal recoil produced by internal combustion.

Satellite. Celestial body that moves in an orbit around a planet. A moon.

Second. Period of time equivalent to 1/86,164.10 sidereal day. Angular measurement equivalent to 1/36000.

Secondary emission. The release of secondary electrons from a metallic surface by an incident beam of primary electrons. Basic principle of the electron-multiplier.

Shooting star. Popular name for the phenomenon of vaporisation of a meteorite by friction with Earth’s atmosphere.

Sidereal day. Time required for Earth to revolve once on its own axis, relative to the fixed stars.

Sidereal year. Time required for the Sun apparently to revolve once on its own axis, relative to the fixed stars.

Sidereal period. Time required for a planet to circle its sun.

Skip distance. Minimum distance from a radio transmitter at which sky waves cannot be received owing to their passage through the ionosphere at a small angle and hence their transmission into space.

Sky wave. A radio wave that passes from the transmitter to receiver by reflection from the ionosphere.

Solar day. Interval between two successive returns of the Sun to the meridian; a variable period, the average of which is the mean solar day.

Solar system. The celestial family that includes the Sun, nine known planets and a belt of asteroids. Any such system would be a solar system.

Solstice. The point at which the Sun is in greatest declination. One solstice occurs towards the end of June, the other towards the end of December.

Sound. A quality attributed by the human auditory association area to the effect of longitudinal pressure waves received through a medium from a vibrating body.

Space-time. A conception arising from the relativity theory in which the former ideas of the independence of three-dimensional space and one-dimensional space-time continuum.

Spectrum. The phenomenon obtained when mixed electromagnetic waves are separated into constituent wavelengths, each wavelength giving a separate image.

Speed. The ratio of the distance traversed by a moving body to the time taken to traverse it, irrespective of direction.

Spin energy. Energy possessed by a sub-atomic particle by virtue of its revolution about its own axis.

Squared circle. An impossible mathematical conception, wherein a square is exactly equal in area to a given circle. Since circle area is computed in terms of the inexact constant pi, it is impossible to construct such a circle.

States. Matter may exist in either the solid, liquid or gaseous states.

Statics. The scientific study of the relation between stationary matter and incident forces.

Stationary state. A quantal condition where only certain energy levels are permissible. Change from one stationary state to another is accompanied by emission or absorption of energy.

Statistics. A system for obtaining theoretical inferences from examination of numerical experimental data.

Stefan’s Law. This states that the heat radiation energy emitted in unit time from a black body of unit area is proportional to the fourth power of its absolute temperature.

Stereochemistry. Study of the properties of molecules that are due to their three-dimensional form.

Stratosphere. The layer of Earth’s atmosphere roughly seven miles up.

Streptomycin. A therapeutically active metabolic product of the fungus Actinomyces.

Stroboscope. Instrument for the periodic illumination of stationary, rotating or vibrating bodies at the same frequency as the body is moving, thus making the bodies appear non-moving.

Subatomic. Term applied to phenomena occurring within the atom, and to particles therein.

Sun. An apparently stationary heavenly body that is incandescent and may or may not be orbited by planets.

Sun-spots. Enormous areas of electromagnetic disturbance on Sol’s surface, visible from Earth as large black patches that occur in large number at eleven-year intervals.

Superheterodyne. A radio circuit that utilises intermediate frequency amplification.

Supersonic. Applied to anything that moves faster than sound (1,100 ft.p.s. in air)–not to sounds that have higher than audible frequency (ultrasonics).

Synchrotron. Electron accelerator that combines the characteristics of the betatron and cyclotron. It is able to raise the velocity of electrons to an extent whereby their mass increases in accordance with the predictions of the relativity theory.

Tanget. On a circle, a straight line making a right-angle with the radius where it touches the circumference. On an angle, the length of the perpendicular divided by the base of a right-angled triangle–giving the tangent of the opposite base angle.

Telemeter. Any device for measuring a phenomenon at a distance.

Temperature. A measure of the degree of kinetic energy of the molecules of a substance. Temperature rises as kinetic energy increases. Molecular kinetic energy constitutes heat.

Temporary magnetism. Magnetism that lasts only so long as the magnetized body remains in a magnetic field.

Tensor. Ration of increase in length of a vector.

Terminal velocity. Constant velocity finally reached by a body moving through a resisting medium under constant force.

Tetrode. A thermionic valve with anode, cathode, control grid and screen grid.

Theorem. An assertion based on logical reasoning from observed facts or from axioms.

Thermion. A charged atom liberated from a hot surface.

Thermionic valve. A sealed vacuum chamber holding a system of electrodes in which electrons pass from a heated cathode to a positively charged anode, intervening grids controlling the current.

Thermistor. An instrument for measuring temperature by virtue of the change in resistance of a semi-conductor with rise or fall of temperature.

Thermocouple. An instrument for measuring temperature by virtue of the electric current generated in a circuit made of two different metallic wires joined at the ends, one end of which is kept at a higher or lower temperature than the other, which is placed at the point where the temperature is to be measure.

Thermodynamics. The scientific study of phenomena involving heat changes.

Thermodynamical Laws. (1) The heat produced when work is transformed into heat is equivalent to the amount of work required for the transformation. (2) Heat cannot be transferred continuously from a body at a lower temperature to a body at a higher temperature. (3) Absolute zero temperature is theoretically impossible to attain.

Thermopile. An alternating series of antimony and bismuth rods that generate current when the junctions are heated, and so may be used as a radiant heat thermometer.

Thermostat. A device which terminates a source of heat when a predetermined temperature is reached, and cuts it in again when the temperature drops below that level.

Transformer. An instrument for converting voltages without change of frequency.

Transistor. A substitute for the thermionic valve, in which a piece of germanium has a plane electrode on one side and two point electrodes on the other.

Transit. Passage of a celestial body across the meridian.

Triode. A thermionic valve with anode, cathode and control grid.

Turbine. A motor in which a bladed wheel is turned by the force of some medium (air, stream, water, etc.) on the blades.

Ultramicroscope. An instrument for detecting very small particles by focussing a beam of light in a liquid obliquely to the direction of observation.

Umbra. The darkest (central) part of a shadow.

Uncertainty principle. This states that both the position and momentum of a particle cannot be accurately determined at the same time, due to the fundamental waviform character of matter.

Universe. Everything that exists.

Vacuum. A theoretical state in which space contains no matter. A perfect vacuum is impossible to attain because the surrounding matter must exert a vapour pressure.

Valency. A measure of the power of combination of an atom or radical expressed as the number of hydrogen atoms that an atom or radicle can combine with or replace.

Variable stars. Stars which undergo changes in luminosity.

Vector. A physical phenomenon that cannot be defined exactly unless a direction is included in the definition.

Velocity. Speed in a stated direction.

Viscosity. Internal friction in a fluid restricting motion within itself.

Vitalistic theory. The idea that all biological phenomena are the result of a vital (i.e., non-material) force, and independent of chemical and physical forces. There is no evidence to support the idea.

Volt. Unit of potential difference.

Watt. Electrical unit of power expressed as the energy used up in a second when a current of one ampere passes through a system with a potential difference of one volt. Watts are the product of volts times amperes.

Wavelength. The distance between equivalent points along a wave, e.g., crests or troughs.

Wave mechanics. A theory of atomic structure put forward by Louis de Broglie in 1924, in which electrons are considered as wave phenomena close to the nucleus and executing oscillations in a series of definite frequencies which correspond to energy levels of the atom. The ‘wave’ however is not regarded as having a real existence, since this would entail a multidimensional hyperspace. Wave terminology is used in order to express the mathematical relations involved.

Wave number. Reciprocal of wavelength, being the number of waves in unit distance.

Work. Phenomenon whereby a force acts on a body in such a way that motion results. If a force F acts on a body and its point of application moves a distance s in a direction making an angle theta with the direction of F, then the force is said to do an amount of work Fcos theta on the body.

X-rays. Electromagnetic waves of length from 5X10-7 to 6X10-10 cm, produced when matter is bombarded by cathode rays.

X-ray spectrum. Individual spectrum produced when an element is bombarded by cathode rays.

Young’s modulus. Ratio of stress to longitudinal strain on a cross-section of a rod or wire.

Zenith. Point on the celestial sphere that is immediately above the observer.

Zodiac. That part of the celestial sphere that contains the paths of Sun, Moon and planets.

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