It is not, however, the purview, or purpose of this book, to incite people to work on the problem of Perpetual Motion, neither is it its purview or purpose to dissuade them from it. In the works of Mr. Dircks, mentioned in the preface of this work, the devices for Perpetual Motion are classified somewhat with reference to the time each was produced. In some instances with reference to whether or not patents were applied for and obtained, or as to the source of information concerning them. A careful examination of the devices presented in Mr. Dirck's two works, and of those, information concerning which has been obtained elsewhere, leads the author to believe that nothing is to be gained by an attempted classification along those lines. In countless instances Perpetual Motion seekers of different races and living in separate countries, and, indeed, on different continents, centuries apart, have sought the attainment of Perpetual Motion by practically the same devices, and inventor after inventor has brought forth alleged inventions depending upon precisely the same underlying mechanical principle. The author has attempted to classify the various devices presented in this book according to the underlying mechanical principles upon which the inventor chiefly relied for the success of his invention. Even this classification is extremely difficult and not well distinguished. Many of them, indeed most of them, depend for their success upon more than one mechanical principle, and the classifications thereby inevitably intermingle and overlap what otherwise would be their distinguishing boundaries. Still it is believed by the author that it is the best that could be adopted, and that no better or clearer classification is possible than the one here presented. The various devices are classified by the author under the following heads: Devices by Means of Wheels and Weights. Devices by Means of Rolling Weights and Inclined Planes. Hydraulic and Hydro-Mechanical Devices. Pneumatic Siphon and Hydro-Pneumatic Devices. Magnetic Devices. Devices Utilizing Capillary Attraction and Physical Affinity. Liquid Air as a Means of Perpetual Motion. Radium and Radio-Active Substances Considered as a Conceived Source of Perpetual Motion. Perpetual Motion Devices Attempting Its Attainment by a Misconception of the Relation of Momentum and Energy. to which is added-- "A Discussion of the Alleged Inventions of the very eminent Edward Sommerset, Sixth Earl and Second Marquis of Worcester, and Jean Ernest Eli-Bessler Orffyreus. Also-- "A Discussion by the Author of the 'Doctrine of Conservation of Energy, and Its Relation to the Possibility of Perpetual Motion.'" And-- "A Discussion by the Author of 'Will Perpetual Motion Ever Be Accomplished?'" CHAPTER I DEVICES BY MEANS OF WHEELS AND WEIGHTS Wilars de Honecort