A visit to the seaside—What is a wave?—Wave-motion on water—Definition of a wave—Sea waves—Various forms of wave-motion—Wave length, velocity, and frequency—Atlantic waves—Rules for speed of sea waves—Illustrations of wave-motion—A stone falling on water—Production of a wave-train—Wave-energy—Conditions for the production of wave-motion—Distinction between wave-velocity and wave-train velocity—Why a wave breaks—Waves in canals—Rule for speed of a canal wave—Falling bodies—A “bore”—Tidal waves—Ripples—Distinction between waves and ripples—Surface tension on liquids—A needle floating on water—Experimental production of ripples—Reflection and refraction of ripples and waves—Interference of waves and ripples—Photography of waves and ripples 1 CHAPTER II. WAVES AND RIPPLES MADE BY SHIPS. Ship-waves—The viscosity of liquids—How it is demonstrated—Rotational and irrotational motion in fluids—Eddies and whirls—Smoke rings—Vortex motion—Professor Hele-Shaw’s experiments—Irrotational or stream-line motion in water—The motion of water round a ship—The motion of water along a pipe—Flow in uniform pipes and non-uniform pipes—Relation between fluid velocity and pressure—Skin resistance and wave-making resistance—The movement of a fish—Motion through a perfect fluid—The waves made by moving objects—Waves made by ducks and swans—Echelon waves—Ship bow waves—The form of ship-waves—Mr. Froude’s experiments—Ship-models and experimental tanks—How a ship is designed—Froude’s laws—Testing ship-models—The design of a racing-yacht—Comparison of British and American yachts—The Cup race—Scott Russell’s experiments on canal-boats 57 CHAPTER III. WAVES AND RIPPLES IN THE AIR. Air necessary for the production of sound—A sounding body is in vibration—Harmonic motion—The difference between noise and music—The nature of an air wave—The physical qualities of air—Longitudinal or compressional waves—Wave-models to illustrate the nature of sound waves—Quality of a sound—Velocity of an air wave—An illustration on a gigantic scale—The voice of a volcano heard round the world—The effect of temperature on air-wave velocity—Comparison of theory and experiment—Circumstances affecting distance at which sounds can be heard—Funeral guns—Fog-signals and sirens—Effect of wind and density—Sensitive flames as sound-detectors—Inaudible sounds—The reflection and refraction of sound waves—A sound-lens and sound-prism—The interference of sounds—Two sounds producing silence—The phonograph—A soap-bubble film set in vibration by air waves 103 CHAPTER IV. SOUND AND MUSIC.