Force perpendicular to a Plane.--Oblique Force.--Inclined Plane.-- Weight produces Pressure and Motion.--Motion uniformly accelerated.-- Space moved through in a given Time.--Increased Elevation produces increased Force.--Perpendicular and horizontal Plane.--Final Velocity.--Motion down a Curve.--Depends upon Velocity and Curvature. --Centrifugal Force.--Circle of Curvature.--Radius of Curvature.-- Whirling Table.--Experiments.--Solar System.--Examples of centrifugal Force. 85 CHAP. IX. THE CENTRE OF GRAVITY. Terrestrial Attraction the combined Action of parallel Forces.-- Single equivalent Force.--Examples.--Method of finding the Centre of Gravity.--Line of Direction.--Globe.--Oblate Spheroid.--Prolate Spheroid.--Cube.--Straight Wand.--Flat Plate.--Triangular Plate.-- Centre of Gravity not always within the Body.--A Ring.--Experiments. --Stable, instable, and neutral Equilibrium.--Motion and Position of the Arms and Feet.--Effect of the Knee-Joint.--Positions of a Dancer. --Porter under a Load.--Motion of a Quadruped.--Rope Dancing.-- Centre of Gravity of two Bodies separated from each other.-- Mathematical and experimental Examples.--The Conservation of the Motion of the Centre of Gravity.--Solar System.--Centre of Gravity sometimes called Centre of Inertia. 107 CHAP. X. THE MECHANICAL PROPERTIES OF AN AXIS. An Axis.--Planets and common spinning Top.--Oscillation or Vibration. --Instantaneous and continued Forces.--Percussion.--Continued Force. --Rotation.--Impressed Forces.--Properties of a fixed Axis.--Movement of the Force round the Axis.--Leverage of the Force.--Impulse perpendicular to, but not crossing, the Axis.--Radius of Gyration.-- Centre of Gyration.--Moment of Inertia.--Principal Axes.--Centre of Percussion. 128 CHAP. XI. OF THE PENDULUM. Isochronism.--Experiments.--Simple Pendulum.--Examples illustrative of.--Length of.--Experiments of Kater, Biot, Sabine, and others.-- Huygens’ Cycloidal Pendulum. 145 CHAP. XII. OF SIMPLE MACHINES. Statics.--Dynamics.--Force.--Power.--Weight.--Lever.--Cord.-- Inclined Plane. 160 CHAP. XIII. OF THE LEVER. Arms.--Fulcrum.--Three Kinds of Levers.--Crow Bar.--Handspike.--Oar. --Nutcrackers.--Turning Lathe.--Steelyard.--Rectangular Lever.-- Hammer.--Load between two Bearers.--Combination of Levers.-- Equivalent Lever. 167 CHAP. XIV. OF WHEEL-WORK.