<P> In the preface of the Principia, Newton wrote: </P> <P> (...) Rational Mechanics will be the sciences of motion resulting from any forces whatsoever, and of the forces required to produce any motion, accurately proposed and demonstrated (...) And therefore we offer this work as mathematical principles of his philosophy . For all the difficulty of philosophy seems to consist in this--from the phenomenas of motions to investigate the forces of Nature, and then from these forces to demonstrate the other phenomena (...) </P> <P> The Principia deals primarily with massive bodies in motion, initially under a variety of conditions and hypothetical laws of force in both non-resisting and resisting media, thus offering criteria to decide, by observations, which laws of force are operating in phenomena that may be observed . It attempts to cover hypothetical or possible motions both of celestial bodies and of terrestrial projectiles . It explores difficult problems of motions perturbed by multiple attractive forces . Its third and final book deals with the interpretation of observations about the movements of planets and their satellites . </P> <P> It shows: </P>

Who wrote the well-known book elements which is the basis for modern geometry