CONTENTS. On the Effect of the Internal Friction of Fluids on the Motion of Pendulums...........1 PART I. Analytical Investigation. SECTION I. Adaptation of the General Equations to the case of the Fluid surrounding a Body which oscillates as a Pendulum. General Laws which follow from the form of the Equations. Solution of the Equations in the case of an Oscillating Plane........11 SECTION II. Solution of the Equations in the case of a Sphere oscillating in a mass of Fluid either unlimited, or confined by a Spherical Envelope concentric with the Sphere in its position of Equilibrium.......22 SECTION HI. Solution of the Equations in the case of an Infinite Cylinder oscillating in an unlimited mass of Fluid, in a direction perpendicular to its axis.....38 SECTION IV. Determination of the Motion of a Fluid about a Sphere which moves uniformly with a small velocity. Justification of the Application of the Solutions obtained in Sections II. and III. to cases in which the extent of Oscillation is not small in comparison with the radius of the Sphere or Cylinder. Discussion of a difficulty which presents itself with reference to the uniform motion of a Cylinder in a Fluid........55 SECTION V. On the effect of Internal Friction in causing the Motion of a Fluid to subside. Application to the case of Oscillatory Waves . . . . . . . .67 PART II. Comparison of Theory and Experiment. SECTION I. Discussion of the Experiments of Baily, Bessel, Coulomb, and Dubuat.......76 SECTION II. Suggestions with reference to future Experiments . 123 An Examination of the possible effect of the Radiation of Heat on the Propagation of Sound.........142