Book excerpt: Nobel laureate Steven Weinberg has written that "all that has happened since 1687 is a gloss on the Principia." Now you too can appreciate the significance of this stellar work, regarded by many as the greatest scientific contribution of all time. Despite its dazzling reputation, Isaac Newton's Philosophiae Naturalis Principia Mathematica, or simply the Principia, remains a mystery for many people. Few of even the most intellectually curious readers, including professional scientists and mathematicians, have actually looked in the Principia or appreciate its contents. Mathematician Pask seeks to remedy this deficit in this accessible guided tour through Newton's masterpiece. Using the final edition of the Principia, Pask clearly demonstrates how it sets out Newton's (and now our) approach to science; how the framework of classical mechanics is established; how terrestrial phenomena like the tides and projectile motion are explained; and how we can understand the dynamics of the solar system and the paths of comets. He also includes scene-setting chapters about Newton himself and scientific developments in his time, as well as chapters about the reception and influence of the Principia up to the present day.