Part 2 — CHAPTER LIV PHYSICS

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)330

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

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.

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 331(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

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) 332that 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.

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 333in 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

334Photography

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