CHAPTER VI.--The Classic Mechanics 92 The Principle of Inertia 93 The Law of Acceleration 97 Anthropomorphic Mechanics 103 The School of the Thread 104 CHAPTER VII.--Relative Motion and Absolute Motion 107 The Principle of Relative Motion 107 Newton's Argument 108 CHAPTER VIII.--Energy and Thermodynamics 115 Energetics 115 Thermodynamics 119 General Conclusions on Part III 123 PART IV. _Nature_ CHAPTER IX.--Hypotheses in Physics 127 The Rôle of Experiment and Generalization 127 The Unity of Nature 130 The Rôle of Hypothesis 133 Origin of Mathematical Physics 136 CHAPTER X.--The Theories of Modern Physics 140 Meaning of Physical Theories 140 Physics and Mechanism 144 Present State of the Science 148 CHAPTER XI.--The Calculus of Probabilities 155 Classification of the Problems of Probability 158 Probability in Mathematics 161 Probability in the Physical Sciences 164 Rouge et noir 167 The Probability of Causes 169 The Theory of Errors 170 Conclusions 172 CHAPTER XII.--Optics and Electricity 174 Fresnel's Theory 174 Maxwell's Theory 175 The Mechanical Explanation of Physical Phenomena 177 CHAPTER XIII.--Electrodynamics 184 Ampère's Theory 184 Closed Currents 185 Action of a Closed Current on a Portion of Current 186 Continuous Rotations 187 Mutual Action of Two Open Currents 189 Induction 190 Theory of Helmholtz 191 Difficulties Raised by these Theories 193 Maxwell's Theory 193 Rowland's Experiment 194 The Theory of Lorentz 196 THE VALUE OF SCIENCE