The Forms of Liquids 1 The Fibres of Corti 17 On the Causes of Harmony 32 The Velocity of Light 48 Why Has Man Two Eyes? 66 On Symmetry 89 On the Fundamental Concepts of Electrostatics 107 On the Principle of the Conservation of Energy 137 On the Economical Nature of Physical Inquiry 186 On Transformation and Adaptation in Scientific Thought 214 On the Principle of Comparison in Physics 236 On the Part Played by Accident in Invention and Discovery 259 On Sensations of Orientation 282 On Some Phenomena Attending the Flight of Projectiles 309 On Instruction in the Classics and the Mathematico-Physical Sciences 338 Appendixes. I. A Contribution to the History of Acoustics 375 II. Remarks on the Theory of Spatial Vision 386 Index 393 THE FORMS OF LIQUIDS. What thinkest thou, dear Euthyphron, that the holy is, and the just, and the good? Is the holy holy because the gods love it, or are the gods holy because they love the holy? By such easy questions did the wise Socrates make the market-place of Athens unsafe and relieve presumptuous young statesmen of the burden of imaginary knowledge, by showing them how confused, unclear, and self-contradictory their ideas were. You know the fate of the importunate questioner. So called good society avoided him on the promenade. Only the ignorant accompanied him. And finally he drank the cup of hemlock--a lot which we ofttimes wish would fall to modern critics of his stamp. What we have learned from Socrates, however,--our inheritance from him,--is scientific criticism. Every one who busies himself with science recognises how unsettled and indefinite the notions are which he has brought with him from common life, and how, on a minute examination of things, old differences are effaced and new ones introduced. The history of science is full of examples of this constant change, development, and clarification of ideas. But we will not linger by this general consideration of the fluctuating character of ideas, which becomes a source of real uncomfortableness, when we reflect that it applies to almost every notion of life. Rather shall we observe by the study of a physical example how much a thing changes when it is closely examined, and how it assumes, when thus considered, increasing definiteness of form.