CHAPTER LIV

PHYSICS [Sidenote: Early Ideas of the World] More than two thousand years ago the poet Lucretius, reviewing the physical knowledge and theories of the Greeks, described, as the Britannica tells us, how “the world was formed by the conjunctions of streams of atoms, which condensed into the earth, with its attendant water, air, and aether, to form a self-contained whole,” and went on to tell how in the changes of infinite time all possible forms of life appeared, but only those fittest to survive persisted. Here we have an unconscious anticipation of the nebular hypothesis and the theory of natural selection, two of the most tremendous of modern speculations. Four hundred years earlier Democritus, the greatest of the Greek natural philosophers, had said: “According to convention there is a sweet and a bitter, and according to convention there is colour. In truth there are atoms and a void.” Democritus came near announcing the doctrines of the indestructibility of matter and the conservation of energy, yet the conventions which he assailed persisted for generations: colour, taste and other qualities of a substance being regarded as of its essence and as much realities as the substance itself. The theories of the Greeks in fact held the field for centuries, until, during the Renaissance, men’s minds attacked the secrets of nature in a more modern spirit. Yet, long as has been its history, physical science, as we know it to-day, is but a few years old, the result of the feverish activity which has been the obsession of the generation now passing (Vol. 24, p. 396). There are many entertaining touches in the historical account of the development of the physical sciences with which this section of the Britannica is enriched, for every branch of the subject has been treated from the historical point of view. The articles, too, have been written by masters who can describe clearly because they see clearly, and no reader, desiring a sound knowledge of the general principles on which science rests, and of the conclusions to which the latest investigations have directed scientific thought, will go away empty handed. The section of the Physical Sciences in the Britannica covers, of course, an enormous field which for general purposes may be conveniently divided into:— (_i_) _Matter and Motion_ (_ii_) _Sound_ (_iii_) _Light_ (_iv_) _Heat_ (_v_) _Electricity and Magnetism_ As a preliminary to any one of these and to the whole subject the reader will be well advised to read the article SCIENCE (Vol. 24, p. 396), by W. C. D. Whetham of Trinity College, Cambridge, author of _Recent Development of Physical Science_; those on UNITS, PHYSICAL (Vol. 27, p. 738), and UNITS, DIMENSIONS OF (Vol. 27, p. 736), are also of fundamental importance; and those on SPACE AND TIME (Vol. 25, p. 525), and TIME, MEASUREMENT OF (Vol. 26, p. 983), may profitably be consulted. (_I_) _Matter and Motion_ [Sidenote: Matter] Since all physical phenomena are manifestations, in one form or other, of matter in motion, this first division of the subject is introductory to all the rest, and should preferably be studied first. The latest theories in connection with the properties of MATTER (Vol. 17, p. 891) are discussed by Sir J. J. Thomson, professor of experimental physics, Cambridge University, who has led the way in the investigation of the electrical theory of matter. The article is directed to the establishment of the electronic theory, and in view of the vast amount of original work which the author has carried out in this field, his treatment in the Britannica should be welcome to all students of physical science. Supplementing this are the following: ELEMENT, by Wilhelm Ostwald (Nobel Prizeman in Chemistry, 1909), especially the concluding remarks (Vol. 9, p. 253); ATOM (Vol. 2, p. 870); ELECTRICITY, _Electronic Theory_ (Vol. 9, p. 192). Early hypotheses are described under SCIENCE (Vol. 24, p. 397); MOLECULES (Vol. 18, p. 654); ALCHEMY (Vol. 1, p. 521); and modern conceptions are discussed under LIQUID GASES, _Cohesion_ (Vol. 16, p. 756); and SPECTROSCOPY (Vol. 25, p. 625). Reference should also be made to the articles DENSITY (Vol. 8, p. 46); DIFFUSION (Vol. 8, p. 255); and especially GRAVITATION (Vol. 12, p. 384), by Professor Poynting of the University of Birmingham, and AETHER (Vol. 1, p. 292), by Sir Joseph Larmor, secretary of the Royal Society. [Sidenote: Motion] The principal articles dealing with motion are: MOTION, LAWS OF (Vol. 18, p. 906), which deals mainly with Newton’s Laws; and ENERGY (Vol. 9, p. 398), and ENERGETICS (Vol. 9, p. 390), both by Sir Joseph Larmor. Of as great importance from the physical point of view are WAVE (Vol. 28, p. 424), the part of the article MECHANICS dealing with simple harmonic motion (Vol. 17, p. 975) and elliptic harmonic motion (p. 978), and HARMONIC ANALYSIS (Vol. 12, p. 956), all by Professor Lamb of the University of Manchester. Other articles which should be consulted are CAPILLARY ACTION (Vol. 5, p. 256), and PERPETUAL MOTION (Vol. 21, p. 180). (_II_) _Sound_ The main article SOUND (Vol. 25, p. 437) is by Prof. J. H. Poynting of the University of Birmingham, and very completely covers the subject; the reader will, however, wish to refer to several other articles for supplementary information. Thus in the article HEARING (Vol. 13, p. 124), the range of audibility is discussed (see also TARTINI, Vol. 26, p. 436, for an account of Tartini’s tones), while with regard to quality of tone the reader will find suggestive matter under VIOLIN (Vol. 28, p. 104). An account of experiments in balloons on the propagation of sound, will be found (Vol. 1, p. 267) under AERONAUTICS. Reference should also be made to the articles WAVE (Vol. 28, p. 425), ELASTICITY, _Vibrations and Waves_ (Vol. 9, p. 158), and HARMONIC ANALYSIS (Vol. 12, p. 956) for a discussion of the form of sound waves. For applications of the principles of sound production, see also the articles PHONOGRAPH (Vol. 21, p. 467), GRAMOPHONE (Vol. 12, p. 333), and especially STRINGED INSTRUMENTS (Vol. 25, p. 1038), WIND INSTRUMENTS (Vol. 28, p. 709), and other articles on musical instruments (see the chapter on _Music_ in this Guide). For accounts of the researches of KUNDT (Vol. 15, p. 946), LAGRANGE (Vol. 16, p. 75) and STOKES (Vol. 25, p. 951), see those articles. (_III_) _Light_ The main article LIGHT (Vol. 16, p. 608) is in four parts. The _Introductory_ and _Historical_ sections are by C. Everitt; that on the _Nature_ of Light by Professor Lorentz of the University of Leiden; that on its _Velocity_ by the late Simon Newcomb, the eminent American astronomer. The different phenomena connected with the subject may conveniently be grouped and studied as follows:— (a) COLOUR (Vol. 6, p. 728); Intensity, see PHOTOMETRY (Vol. 21, p. 525), a brilliant article by Prof. H. H. Turner, of Oxford University; ILLUMINATION (Vol. 14, p. 320). (b) REFLECTION OF LIGHT (Vol. 23, p. 2); ABSORPTION (Vol. 1, p. 76); REFRACTION (Vol. 23, p. 25); DISPERSION (Vol. 8, p. 315); INTERFERENCE (Vol. 14, p. 685); POLARIZATION OF LIGHT (Vol. 21, p. 932). (c) SHADOW (Vol. 24, p. 738); DIFFRACTION (Vol. 8, p. 238); CALORESCENCE (Vol. 5, p. 60); FLUORESCENCE (Vol. 10, p. 375); PHOSPHORESCENCE (Vol. 21, p. 476). (d) MIRROR (Vol. 18, p. 575); LENS (Vol. 16, p. 421); CAUSTIC (Vol. 5, p. 558); ABERRATION (Vol. 1, p. 54). (e) CORONA (Vol. 7, p. 184); HALO (Vol. 12, p. 864); MIRAGE (Vol. 18, p. 573); RAINBOW (Vol. 22, p. 861); SKY (Vol. 25, p. 202); TWILIGHT (Vol. 26, p. 492)—see also DUST (Vol. 8, p. 713). (f) TELESCOPE (Vol. 26, p. 557); MICROSCOPE (Vol. 18, p. 392); OBJECTIVE (Vol. 19, p. 948); CAMERA LUCIDA (Vol. 5, p. 104); CAMERA OBSCURA (Vol. 5, p. 104); BINOCULAR INSTRUMENT (Vol. 3, p. 949); STEREOSCOPE (Vol. 25, p. 895). (g) VISION (Vol. 28, p. 130). Far reaching developments are described in PHOTOGRAPHY (Vol. 21, p. 485) and SPECTROSCOPY (Vol. 25, p. 619). In the former article Sir W. de W. Abney describes in great detail photographic _Processes_; Major-General Waterhouse, _Apparatus_ and _Lenses_, while A. H. Hinton discusses the _Pictorial_ aspect of the subject. There are also valuable articles on CELESTIAL PHOTOGRAPHY (Vol. 21, p. 523), by Professor Turner, and on the SPECTROHELIOGRAPH (Vol. 25, p. 618), by the inventor, G. E. Hale, director of the Solar Observatory of the Carnegie Institution at Mount Wilson, Cal. The relation between magnetism and light is discussed in an article MAGNETO-OPTICS (Vol. 17, p. 388), by Sir J. J. Thomson. (_IV_) _Heat_ The treatment of this subject in the Encyclopaedia Britannica has been generally organized by Prof. H. L. Callendar, of the Royal College of Science, London, who was designated by Lord Kelvin as his successor in this department of the work. In pursuing the subject the following order may conveniently be followed: (a) HEAT (Vol. 13, p. 135), THERMOMETRY (Vol. 26, p. 821), CALORIMETRY (Vol. 5, p. 60), and THERMODYNAMICS (Vol. 26, p. 808), all by Professor Callendar; COLD (Vol. 6, p. 663). (b) CONDUCTION OF HEAT (Vol. 6, p. 890); RADIATION, THEORY OF (Vol. 22, p. 785); RADIOMETER (Vol. 22, p. 806). (c) FUSION (Vol. 11, p. 369); VAPORIZATION (Vol. 27, p. 897); CONDENSATION OF GASES (Vol. 6, p. 844); LIQUID GASES (Vol. 16, p. 744); THERMOELECTRICITY (Vol. 26, p. 814). (_V_) _Electricity and Magnetism_ [Sidenote: Historical] We are so accustomed to think of electricity as the peculiar possession of our own age (the first crude attempts at an electric light were only two score years ago) that we are apt to forget that the first experiments in the science were made at least 2500 years ago. The first effort to place it on a true experimental and inductive basis dates back more than three centuries to the publication of the researches of WILLIAM GILBERT (see Vol. 12, p. 9), the most distinguished man of science of his time, whom Queen Elizabeth appointed her private physician at the “usual” salary of £100. A hundred years later, VOLTA (Vol. 28, p. 198), who might be called the patron saint of electricity, produced the first electric current with the pile which bears his name. Meanwhile BENJAMIN FRANKLIN (Vol. 11, p. 30) had been experimenting with his famous kite, and CAVENDISH (Vol. 5, p. 580) and COULOMB (Vol. 7, p. 508) had been paving the way for the startling developments which resulted from Volta’s invention. In the 19th century FARADAY (Vol. 10, p. 173), AMPÈRE (Vol. 1, p. 878), OHM (Vol. 20, p. 34), LORD KELVIN (Vol. 15, p. 721), JAMES CLERK MAXWELL (Vol. 17, p. 929) and other brilliant investigators in rapid succession developed the field, until the science and application of electricity have attained a position absolutely dominating our daily life. [Sidenote: Analysis of the Subject] The section of the Britannica treating this great subject is therefore one of the most important in the whole work, and it was in the fullest recognition of the fact that the editor asked Prof. J. A. Fleming, of the University of London, famous for his original work in both the mathematical and the experimental branches of the science, to organize the sections for the new edition. The ground is generally covered in the four articles, on electricity, electrostatics, electrokinetics, and electromagnetism, all contributed by Prof. Fleming himself. The article ELECTRICITY (Vol. 9, p. 179) is the key article to the subject, and should be read first. The two great branches of electrical theory then follow: (a) ELECTROSTATICS (Vol. 9, p. 240), in connection with which the article ELECTRICAL MACHINE (Vol. 9, p. 176) should also be studied, with reference to ELECTROSCOPE (Vol. 9, p. 239) and ELECTROPHORUS (Vol. 9, p. 237). (b) ELECTROKINETICS (Vol. 9, p. 210) and, supplementing it, CONDUCTION, ELECTRIC (Vol. 6, p. 855). The latter is divided into three parts: (i.) _Conduction in Solids_, by Prof. Fleming; (ii.) _Conduction in Liquids_ by W. C. D. Whetham; (iii.) _Conduction in Gases_, by Sir J. J. Thomson. In connection with (ii.) should be read ELECTROLYSIS (Vol. 9, p. 217), by W. C. D. Whetham, and with (iii.) RÖNTGEN RAYS (Vol. 23, p. 694) and VACUUM TUBE (Vol. 27, p. 834), both by Sir J. J. Thomson, whose article ELECTRIC WAVES (Vol. 9, p. 203) is of fundamental importance. The general principles of electrical engineering are set out in the article ELECTRIC SUPPLY (Vol. 9, p. 193) with reference to DYNAMO (Vol. 8, p. 764); MOTORS, ELECTRIC (Vol. 18, p. 910); TRANSFORMERS (Vol. 27, p. 173); ACCUMULATOR (Vol. 1, p. 126); POWER TRANSMISSION, _Electric_ (Vol. 22, p. 233); TRACTION, _Electric Traction_ (Vol. 27, p. 120); LIGHTING, _Electric_ (Vol. 16, p. 659); see also ELECTROCHEMISTRY (Vol. 9, p. 208) and ELECTROMETALLURGY (Vol. 9, p. 232); TELEGRAPH (Vol. 26, p. 510); TELEPHONE (Vol. 26, p. 547). A bridge to MAGNETISM (Vol. 17, p. 321), an article by Shelford Bidwell, former president of the Physical Society, is the article ELECTROMAGNETISM (Vol. 9, p. 226), by Prof. Fleming. This article leads also to the study of manifestations in nature of electricity and magnetism: see the articles ATMOSPHERIC ELECTRICITY (Vol. 2, p. 860); AURORA POLARIS (Vol. 2, p. 927); EARTH CURRENTS (Vol. 8, p. 813); and MAGNETISM, TERRESTRIAL (Vol. 17, p. 353); and to the applications of its principles in the COMPASS (Vol. 6, p. 804). An alphabetical list of the articles in the Britannica on the subjects treated in this chapter is given below. The biographies of distinguished physicists, included in the list, are valuable as containing accounts of their contributions to science, and are full of human interest. ARTICLES ON THE PHYSICAL SCIENCES IN THE BRITANNICA, INCLUDING THOSE ON FAMOUS PHYSICISTS Aberration Absorption of Light Accumulator Achromatism Acoustics Acre Actinometer Adhesion Aepinus, F. U. T. Aether, or Ether Aggregation Agonic Lines Aldini, Giovanni Alhazen Amontons, Guillaume Ampère, A. M. Amperemeter or Ammeter Anderson, John Angström, A. J. and K. J. Aperture Arago, D. F. J. Armature Arnaldus de Villa Nova Arrhenius, S. A. As Atmospheric Electricity Atwood, George Auncel Avogadro, Amedeo Avoirdupois Ayrton, W. E. Bache, Alexander D. Baker, Henry Balance Barleycorn Barometer Barometric Light Barrel Battery Beccaria, G. B. Becquerel (family) Bell, A. Graham Binocular Instrument Biot, Jean Baptiste Boyle, Robert Brewster, Sir David Bushel Cagniard de la Tour, C. Calibration Calorescence Calorimetry Camera Lucida Camera Obscura Canton, John Capillary Action Carat Carnot, Sadi N. L. Carucate Caustic Cavallo, Tiberius Cinematograph Claudet, A. F. J. Clausius, Rudolf J. E. Cold Colour Compass Condensation of Gases Conduction, Electric Conduction of Heat Cornu, Marie Alfred Coulomb, C. A. Curie, Pierre Cyclometer Daguerre, L. J. M. Dallmeyer, John Henry De la Rive, A. A. Della Porta, G. Battista Demijohn Density Diamagnetism Dielectric Diffraction of Light Diffusion Dimension Dispersion Dolland, John Duhamel, J. B. Dynamo Earth Currents Edison, T. A. Electrical or Electrostatic Machine Electricity Electricity Supply Electric Waves Electrochemistry Electrokinetics Electrolysis Electromagnetism Electrometallurgy Electrometer Electron Electrophorus Electroplating Electroscope Electrostatics Electrotyping Energetics Energy Erman, Paul Fahrenheit, G. D. Fathom Fizeau, A. H. L. Fluorescence Forbes, James David Forman, Simon Foucault, J. B. L. Fraunhofer, J. von Fresnel, Augustin J. Furlong Fusion Fuze, or Fuse Gallon Galvanometer Geissler, Heinrich Gibbs, J. W. Gilbert, or Gylberde, W. Glaisher, James Graduation Gramophone Gravitation Gray, Elisha Grove, Sir William R. Guericke, Otto von Harris, Sir W. S. Hearing Heat Heliostat Helmholtz, H. L. F. von Henry, Joseph Hertz, Heinrich R. Hogshead Hooke, Robert Hopkinson, John Hour-glass Hughes, D. E. Hydrometer Hypsometer Hysteresis Illumination Inch Inclinometer Induction Coil Interference of Light Jablochkov, Paul Joule, J. P. Kaleidoscope Kater, Henry Kelvin, 1st baron Kirchhoff, G. R. König, K. R. Kundt, A. A. E. E. Lambert, J. H. Langley, S. P. Lantern Lens Leyden Jar, or Condenser Lichtenberg, G. C. Light Lighting Lightning Conductor Liquid Gases Lodge, Sir Oliver J. Magnetism Magnetism, Terrestrial Magnetograph Magnetometer Magneto-Optics Malus, E. L. Manometer Mariotte, Edme Marum, Martin van Matter Matteucci, Carlo Maxwell, J. Clerk Mayer, Julius R. Melloni, Macedonio Meter, Electric Metric System Michell, John Microscope Mirror Model Molecule Morgen Morse, S. F. B. Motion, Laws of Motors, Electric Musschenbroek, P. van Neckam, A. Nicholson, W. Nicol, William Niepce, J. Nicéphore Nobili, Leopoldo Nollet, Jean Antoine Objective, or Object Glass Ohm, Georg Simon Ohmmeter Olmsted, Denison Optics Oscillograph Ounce Papin, Denis Peck Peltier, J. C. A. Permeability, Magnetic Permeameter Perpetual Motion Phonograph Phosphorescence Photography Photometry Pint Plateau, J. A. F. Pneumatics Poggendorff, J. C. Polarity Polarization of Light Pood Potentiometer Pound Power Transmission Prévost, Pierre Pyrometer Radiation, Theory of Radiometer Rayleigh, Lord Reflection of Light Refraction Rod Röntgen Rays Röntgen, W. K. Rowland, Henry A. Rumford, Count Saussure, H. B. de Science Shadow Siemens, E. Werner von Sky Sound Space and Time Spectacles Spectroscopy Speculum Spherometer Standard Stereoscope Stewart, Balfour Sun or Photo Copying Swan, Sir Joseph W. Tait, Peter G. Talbot, W. H. Fox Talent Tartini, G. Telegraph Telephone Thermodynamics Thermoelectricity Thermometry Thomson, James Torricelli, E. Transformers Trumpet, Speaking and Hearing Tyndall, John Units, Dimensions of Units, Physical Vacuum Tube Vaporization Vision Volta, Alessandro Voltmeter Wattmeter Wave Weber, W. E. Weighing Machines Weights and Measures Wheatstone’s Bridge Wheatstone, Sir Chas. Wiedemann, G. H. Young, Thomas