Works of Tyros Known to Author; Momentum Defined, Differentiated, Measured and Explained; Energy Defined, Differentiated, Measured and Explained; Explanation by Author of Common Misconception of the Relation of Momentum and Energy and Attempts to thus Realize Perpetual Motion; the Fallacy Explained by Illustrations of Energy Required for and Represented by Acceleration and Retardation of Velocity; Property of Numbers Relating to; Arithmetical Progression Illustration 200-211 CHAPTER X--THE ALLEGED INVENTIONS OF EDWARD SOMMERSET, SIXTH EARL AND SECOND MARQUIS OF WORCESTER, AND OF JEAN ERNEST ELI-BESSLER (COUNCILLOR) ORFFYREUS-- Intense Interest Caused by; Notice of Marquis of Worcester and Councillor Orffyreus and Periods in Which They Lived; Description by Marquis of Worcester of the Essentials of His Claimed Inventions; Excerpts From Remarks of Councillor Orffyreus on His Claimed Invention; Dedication by Councillor Orffyreus to God, the Public, to Men of Learning and to Himself as the Discoverer; Article Concerning the Orffyrean Wheel Published 1720 in Gentlemen's Magazine; Criticism by "A Constant Reader" of Attitude of W. Kenrick Concerning the Orffyrean Wheel; Article by Rev. J. T. Desagulier Concerning the Device of Marquis of Worcester and the Orffyrean Wheel; Excerpt from Dr. William Kenrick's Lecture on Perpetual Motion; De la Hire's Remarks Concerning Perpetual Motion; Letter from Prof. 's Gravesande to Sir Isaac Newton; Animadversions of Prof. Alliman on the Neglect of the Orffyrean inventions; Dr. Charles Hutton's Scientific Works and Notice of the Orffyrean Wheel; Remarks by the Author on the Historical Celebrity of These Inventions 212-255 CHAPTER XI--CONSERVATION OF ENERGY. A DISCUSSION OF THE RELATION OF THE DOCTRINE OF CONSERVATION OF ENERGY, AND THE POSSIBILITY OF PERPETUAL MOTION-- Statement of Doctrine of Conservation of Energy; Upon What Proof of Doctrine Rests; Not Mathematically Proved; Conforms to Natural Phenomena; Multiplied Illustrations; Inter-changeability and Convertibility of Heat with Mechanical and Other Forms of Energy; Explanation of Heat and Energy Units, and Their Relative Equivalents; British Thermal Unit, Foot-Pound and Horse-Power and Their Mutual Relationship Explained; Further Illustrations; Galileo's Famous Pendulum Experiment; Apparent Anticipation of the Principle of Conservation of Energy 256-269 CHAPTER XII--WILL PERPETUAL MOTION EVER BE ACCOMPLISHED?--