Regretfully, this revised edition [of Nine Planets] did not benefit from a few corrections and clarifications which prevent the book from being rated far better. For instance, defining "mass" as "giving information about the relative number of molecules contained in a subject" leaves much unsaid and conveys little accurate information. Similarly, the author produces confusion in the concepts of force and motion and has difficulty with some of his geometric descriptions. But on balance, much is very good and some parts excellent in his concise, systematic historical and descriptive treatment of each of the planets in the solar system.