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EDITOR'S PREFATORY NOTE

THE EVOLUTION OF PHYSICS

Revolutionary change in modern Physics only apparent: evolution not revolution the rule in Physical Theory-- Revival of metaphysical speculation and influence of Descartes: all phenomena reduced to matter and movement-- Modern physicists challenge this: physical, unlike mechanical, phenomena seldom reversible--Two schools, one considering experimental laws imperative, the other merely studying relations of magnitudes: both teach something of truth--Third or eclectic school-- Is mechanics a branch of electrical science?

MEASUREMENTS

? 1. Metrology: Lord Kelvin's view of its necessity-- Its definition

? 2. The Measure of Length: Necessity for unit-- Absolute length--History of Standard--Description of Standard Metre--Unit of wave-lengths preferable--The International Metre

? 3. The Measure of Mass: Distinction between mass and weight--Objections to legal kilogramme and its precision--Possible improvement

? 4. The Measure of Time: Unit of time the second--Alternative units proposed--Improvements in chronometry and invar

? 5. The Measure of Temperature: Fundamental and derived units--Ordinary unit of temperature purely arbitrary--Absolute unit mass of H at pressure of 1 m. of Hg at 0? C.--Divergence of thermometric and thermodynamic scales--Helium thermometer for low, thermo-electric couple for high, temperatures--Lummer and Pringsheim's improvements in thermometry.

? 6. Derived Units and Measure of Energy: Importance of erg as unit--Calorimeter usual means of determination--Photometric units.

? 7. Measure of Physical Constants: Constant of gravitation--Discoveries of Cavendish, Vernon Boys, E?tv?s, Richarz and Krigar-Menzel--Michelson's improvements on Fizeau and Foucault's experiments-- Measure of speed of light.

PRINCIPLES

? 1. The Principles of Physics: The Principles of Mechanics affected by recent discoveries--Is mass indestructible?--Landolt and Heydweiller's experiments --Lavoisier's law only approximately true--Curie's principle of symmetry.

? 2. The Principle of the Conservation of Energy: Its evolution: Bernoulli, Lavoisier and Laplace, Young, Rumford, Davy, Sadi Carnot, and Robert Mayer--Mayer's drawbacks--Error of those who would make mechanics part of energetics--Verdet's predictions--Rankine inventor of energetics--Usefulness of Work as standard form of energy--Physicists who think matter form of energy-- Objections to this--Philosophical value of conservation doctrine.

? 3. The Principle of Carnot and Clausius: Originality of Carnot's principle that fall of temperature necessary for production of work by heat-- Clausius' postulate that heat cannot pass from cold to hot body without accessory phenomena--Entropy result of this--Definition of entropy--Entropy tends to increase incessantly--A magnitude which measures evolution of system--Clausius' and Kelvin's deduction that heat end of all energy in Universe--Objection to this-- Carnot's principle not necessarily referable to mechanics --Brownian movements--Lippmann's objection to kinetic hypothesis.

? 4. Thermodynamics: Historical work of Massieu, Willard Gibbs, Helmholtz, and Duhem--Willard Gibbs founder of thermodynamic statics, Van t'Hoff its reviver--The Phase Law--Raveau explains it without thermodynamics.

? 5. Atomism: Connection of subject with preceding Hannequin's essay on the atomic hypothesis--Molecular physics in disfavour--Surface-tension, etc., vanishes when molecule reached--Size of molecule--Kinetic theory of gases--Willard Gibbs and Boltzmann introduce into it law of probabilities--Mean free path of gaseous molecules--Application to optics--Final division of matter.

THE VARIOUS STATES OF MATTER

? 1. The Statics of Fluids: Researches of Andrews, Cailletet, and others on liquid and gaseous states-- Amagat's experiments--Van der Waals' equation--Discovery of corresponding states--Amagat's superposed diagrams--Exceptions to law--Statics of mixed fluids-- Kamerlingh Onnes' researches--Critical Constants-- Characteristic equation of fluid not yet ascertainable.

? 2. The Liquefaction of Gases and Low Temperatures: Linde's, Siemens', and Claude's methods of liquefying gases--Apparatus of Claude described--Dewar's experiments--Modification of electrical properties of matter by extreme cold: of magnetic and chemical-- Vitality of bacteria unaltered--Ramsay's discovery of rare gases of atmosphere--Their distribution in nature--Liquid hydrogen--Helium.

? 3. Solids and Liquids: Continuity of Solid and Liquid States--Viscosity common to both--Also Rigidity-- Spring's analogies of solids and liquids--Crystallization --Lehmann's liquid crystals--Their existence doubted --Tamman's view of discontinuity between crystalline and liquid states.

? 4. The Deformation of Solids: Elasticity-- Hoocke's, Bach's, and Bouasse's researches--Voigt on the elasticity of crystals--Elastic and permanent deformations--Brillouin's states of unstable equilibria--Duhem and the thermodynamic postulates-- Experimental confirmation--Guillaume's researches on nickel steel--Alloys.

SOLUTIONS AND ELECTROLYTIC DISSOCIATION

? 1. Solution: Kirchhoff's, Gibb's, Duhem's and Van t'Hoff's researches.

? 2. Osmosis: History of phenomenon--Traube and biologists establish existence of semi-permeable walls--Villard's experiments with gases--Pfeffer shows osmotic pressure proportional to concentration-- Disagreement as to cause of phenomenon.

? 3. Osmosis applied to Solution: Van t'Hoff's discoveries--Analogy between dissolved body and perfect gas--Faults in analogy.

? 4. Electrolytic Dissociation: Van t'Hoff's and Arrhenius' researches--Ionic hypothesis of--Fierce opposition to at first--Arrhenius' ideas now triumphant --Advantages of Arrhenius' hypothesis--"The ions which react"--Ostwald's conclusions from this--Nernst's theory of Electrolysis--Electrolysis of gases makes electronic theory probable--Faraday's two laws--Valency-- Helmholtz's consequences from Faraday's laws.

THE ETHER

? 1. The Luminiferous Ether: First idea of Ether due to Descartes--Ether must be imponderable--Fresnel shows light vibrations to be transverse--Transverse vibrations cannot exist in fluid--Ether must be discontinuous.

? 2. Radiations: Wave-lengths and their measurements--Rubens' and Lenard's researches-- Stationary waves and colour-photography--Fresnel's hypothesis opposed by Neumann--Wiener's and Cotton's experiments.

? 3. The Electromagnetic Ether: Amp?re's advocacy of mathematical expression--Faraday first shows influence of medium in electricity--Maxwell's proof that light-waves electromagnetic--His unintelligibility--Required confirmation of theory by Hertz.

? 4. Electrical Oscillations: Hertz's experiments-- Blondlot proves electromagnetic disturbance propagated with speed of light--Discovery of ether waves intermediate between Hertzian and visible ones--Rubens' and Nichols' experiments--Hertzian and light rays contrasted--Pressure of light.

? 5. The X-Rays: R?ntgen's discovery--Properties of X-rays--Not homogeneous--Rutherford and M'Clung's experiments on energy corresponding to--Barkla's experiments on polarisation of--Their speed that of light--Are they merely ultra-violet?--Stokes and Wiechert's theory of independent pulsations generally preferred--J.J. Thomson's idea of their formation-- Sutherland's and Le Bon's theories--The N-Rays-- Blondlot's discovery--Experiments cannot be repeated outside France--Gutton and Mascart's confirmation-- Negative experiments prove nothing--Supposed wave-length of N-rays.

? 6. The Ether and Gravitation: Descartes' and Newton's ideas on gravitation--Its speed and other extraordinary characteristics--Lesage's hypothesis--Cr?mieux' experiments with drops of liquids--Hypothesis of ether insufficient.

WIRELESS TELEGRAPHY

? 1. Histories of wireless telegraphy already written, and difficulties of the subject.

? 2. Two systems: that which uses the material media , and that which employs ether only.

? 3. Use of earth as return wire by Steinheil --Morse's experiments with water of canal--Seine used as return wire during siege of Paris--Johnson and Melhuish's Indian experiments--Preece's telegraph over Bristol Channel--He welcomes Marconi.

? 4. Early attempts at transmission of messages through ether--Experiments of Rathenau and others.

? 5. Forerunners of ether telegraphy: Clerk Maxwell and Hertz--Dolbear, Hughes, and Graham Bell.

? 6. Telegraphy by Hertzian waves first suggested by Threlfall--Crookes', Tesla's, Lodge's, Rutherford's, and Popoff's contributions--Marconi first makes it practicable.

? 7. The receiver in wireless telegraphy--Varley's, Calzecchi--Onesti's, and Branly's researches-- Explanation of coherer still obscure.

? 8. Wireless telegraphy enters the commercial stage-- Defect of Marconi's system--Braun's, Armstrong's, Lee de Forest's, and Fessenden's systems make use of earth-- Hertz and Marconi entitled to foremost place among discoverers.

THE CONDUCTIVITY OF GASES AND THE IONS

? 1. The Conductivity of Gases: Relations of matter to ether cardinal problem--Conductivity of gases at first misapprehended--Erman's forgotten researches--Giese first notices phenomenon--Experiment with X-rays-- J.J. Thomson's interpretation--Ionized gas not obedient to Ohm's law--Discharge of charged conductors by ionized gas.

? 2. The Condensation of water-vapour by Ions: Vapour will not condense without nucleus--Wilson's experiments on electrical condensation--Wilson and Thomson's counting experiment--Twenty million ions per c.cm. of gas--Estimate of charge borne by ion-- Speed of charges--Zeleny's and Langevin's experiments--Negative ions 1/1000 of size of atoms--Natural unit of electricity or electrons.

? 3. How Ions are Produced: Various causes of ionization--Moreau's experiments with alkaline salts--Barus and Bloch on ionization by phosphorus vapours--Ionization always result of shock.

? 4. Electrons in Metals: Movement of electrons in metals foreshadowed by Weber--Giese's, Riecke's, Drude's, and J.J. Thomson's researches--Path of ions in metals and conduction of heat--Theory of Lorentz--Hesehus' explanation of electrification by contact--Emission of electrons by charged body-- Thomson's measurement of positive ions.

CATHODE RAYS AND RADIOACTIVE BODIES

? 1. The Cathode Rays: History of discovery--Crookes' theory--Lenard rays--Perrin's proof of negative charge--Cathode rays give rise to X-rays--The canal rays--Villard's researches and magneto-cathode rays-- Ionoplasty--Thomson's measurements of speed of rays-- All atoms can be dissociated.

? 2. Radioactive Substances: Uranic rays of Niepce de St Victor and Becquerel--General radioactivity of matter--Le Bon's and Rutherford's comparison of uranic with X rays--Pierre and Mme. Curie's discovery of polonium and radium--Their characteristics--Debierne discovers actinium.

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