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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