rrent, upon the phenomena of magnetism,
or upon all the applications which belong to the domain of
Electrotechnics.

L. POINCARE.

Contents

EDITOR'S PREFATORY NOTE

AUTHOR'S PREFACE

TABLE OF CONTENTS

CHAPTER I

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?

CHAPTER II

MEASUREMENTS

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

Sec. 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

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

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

Sec. 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 deg. C.--Divergence of thermometric
and thermodynamic scales--Helium thermometer for low,
thermo-electric couple for high, temperatures--Lummer
and Pringsheim's improvements in thermometry.

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

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

CHAPTER III

PRINCIPLES

Sec. 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.

Sec. 2. The Principle of the Conservation of Energy:
Its evolution: Bernoulli, Lavoisier and Laplace, Young,
Rumford,