This book is a translation of the 6th to 8th edition of the author's Kleines Lehrbuch der Physik. The circle of readers to which it hopes to appeal and the author's purpose in writing it have been set out in the Preface to the first German edition, published in 1948. The present book consistently follows the principles of the theory of quantities, the beginnings of which date back to James C. Maxwell. This means that in all equations in this book the symbols invariably stand for physical quantities and not for the numerical values of quantities. Only then are the equations gene rally valid and independent of the choice of units used in their evaluation. The units used are always the "metric" units which have been gaining ground increasingly also in the English-speaking countries. A conversion table for some of the more important Anglo-American units is given on page XIV. I would like to record my sincere gratitude to Mr. Ewald Osers for his pains­ taking work in making this translation and to Mr. P. C. Banbury, Ph. D., of the Department of Physics, University of Reading, England, both for the advice he has given hirn throughout and for devising the problems specially for this edition.

Physics.- Quantities. Units.- Scalars and vectors.- Physical equations. Physical laws. Definition.- One Mechanics of Point Masses and Rigid Bodies.- I. Geometry. Kinematics.- Point masses. Rigid bodies. Translation and rotation.- Quantities and units of geometry and kinematics.- Rectilinear uniform motion. Velocity. Acceleration.- Curvilinear motion.- Uniform circular motion.- II. Dynamics.- Forces.- Force and mass.- Gravity and weight. The practical system of units.- Measuring forces and masses.- Point of application of a force.- Composition and resolution of forces.- Pressure and tension.- The reciprocal action theorem.- Reaction.- The center of gravity. Theorem of the center of gravity.- Momentum. The theorem of momentum.- Inertial forces.- Inertial systems. The principle of relativity.- Free fall and projectiles.- III. Work and Energy.- Work.- Energy.- Power.- Equilibrium.- Impact.- Mass and energy.- Friction.- IV. Motion in a Circle. Couples. Harmonic Motion.- Centripetal force.- Centrifugal force.- Moment of inertia.- Couples and torques.- Couples in equilibrium. Levers.- The balance.- Angular momentum.- Oscillations.- The pendulum.- V. Gravitation.- The law of gravitation.- The motion of the moon and the planets.- The tides.- Fields of force.- Problems.- Two Mechanics of Substances.- I. Structure and General Mechanical Properties of Substances.- The building bricks of substances.- States of matter.- Crystals.- Density. Specific volume. Specific weight.- Elasticity of solids.- Linear stretching and compression.- Shear.- Deformation beyond the elastic limit.- Surface tension.- Capillarity.- II. Mechanics of Liquids and Gases at Rest.- Pressure in a liquid.- Liquids under the influence of gravity.- Buoyancy and flotation.- Molecular mechanics. Amount of substance. Mole.- Fundamentals of gas theory.- Diffusion.- Ideal gases.- Pressure of ideal gases.- The characteristic equation for an ideal gas.- Gases under the influence of gravity. Atmospheric pressure.- Vacuum techniques.- III. Mechanics of Flowing Liquids and Gases.- General considerations.- Bernouille's law.- Vortices. Turbulence.- Airfoils.- Viscosity.- Internal friction.- IV. Waves and Oscillations.- Surface waves.- Generalization of the wave concept.- Harmonic waves.- Longitudinal waves.- Transverse waves.- The Doppler effect.- Reflection of waves.- Refraction.- Interference.- Standing waves.- Beats.- Huygens'principle.- Diffraction.- Free vibrations.- Vibration of rods, strings and plates.- Forced vibrations. Resonance.- Oscillating quartz crystals. Ultrasonic waves.- Tones, sounds, noises.- The musical scale.- Hearing. Song and speech.- Problems.- Three Heat.- I. The Nature of Heat. Temperature. Quantity of Heat.- The nature of heat.- The first law of thermodynamics.- Temperature.- The equation of state for an ideal gas. The Kelvin scale.- The centigrade scale.- The thermal expansion of solids and liquids.- Temperature measurement. Very high and very low temperatures.- Thermal capacity.- The specific thermal capacity of gases.- Adiabatic changes of the state of a gas.- Heat exchange.- II. Changes of Phase.- Conversion temperatures.- Fusion.- Vaporization and condensation 126-Boiling.- The liquefaction of gases.- Solutions.- Absorption and adsorption.- III. Heat and Work.- Conversion of mechanical energy into heat.- The second law of thermodynamics.- Conversion of heat into mechanical work.- Sources of heat.- Problems.- Four Electrostatics. Electric Currents.- I. Electrostatics.- Quantity of electricity. Electric charge.- Coulomb's first law.- Elementary electric charge.- Conductors and non-conductors.- Electric fields.- Potential difference.- Electric field strength and potential in conductors.- Distribution of charges on conductors. Electrostatic induction.- Electroscope and electrometer.- Electric displacement. Electric flux. Space charges.- Capacitance.- Capacitors.- Dielectrics.- II. Electric Currents in Solid and Liquid Conductors.- Electric currents.- Resistance. Ohm's law.- Conductors in series and in parallel. Potential and current division.- Measurement of resistances.- The variation of resistance with temperature.- Super-conductivity.- Work done by a current. Heating effect of a current.- Contact potential difference. Thermoelectricity.- "Open circuit" and terminal potential difference of cells.- Conductivity of liquids.- Dissociation.- Chemical reaction at the electrodes.- Faraday's laws.- Electrolytic polarization.- Primary cells. Accumulators.- III. Electric Currents in Gases.- Electric currents in a high vacuum. Hot cathodes.- Thermionic tubes.- Electric currents in gases.- Spontaneous discharge at high pressures.- Glow discharge.- Atmospheric electricity.- Problems.- Five Magnetism and Electrodynamics.- I. Magnets. Magnetic Fields.- Magnets.- Coulomb's second law.- The magnetic field.- A dipole in a magnetic field.- Magnetic flux density. Magnetic flux.- The earth's magnetic field.- II. Electromagnetic Interactions (Electrodynamics).- The magnetic field due to an electric current.- The screw rule.- The fundamental law of electrodynamics.- Electrodynamic quantities and systems of electrodynamic units.- The magnetic field due to a linear current. Magnetomotive force.- The magnetic field inside a solenoid.- Moving charges in a magnetic field.- The force exerted by a magnetic field on a current.- The magnetic moment of a current loop.- The mutual action of currents.- Instruments for measuring current and potential difference.- Electromagnetic induction in moving conductors.- Electromagnetic induction in conductors at rest.- The law of electromagnetic induction.- Electromagnetic induction in an open circuit.- Eddy currents.- Mutual induction.- Self induction.- The induction coil.- Displacement currents.- Electromagnetic fields.- III. The Magnetic Properties of Substances.- Paramagnetism and diamagnetism.- Susceptibility. Permeability.- Electric and magnetic behavior of substances compared.- Ferromagnetism.- The nature of ferromagnetism.- Hysteresis.- Iron in a magnetic field.- IV. Alternating Current. Electrical Oscillations and Waves.- Alternating current.- Impedance in an alternating current circuit.- Alternating current power.- Transformers.- Electrical machines.- Electrical oscillations.- Vacuum tube oscillators.- Electromagnetic waves.- Problems.- Six Light and General Radiation Physics.- I. General.- Models of light.- Rectilinear propagation of light.- The speed of light in a vacuum.- Photometry.- II. Geometrical Optics.- Reflection of light.- The formation of images.- Formation of images by plane mirrors.- Spherical mirrors.- Formation of images by concave mirrors.- Formation of images by convex mirrors.- Refraction of light.- Refraction by a parall…