Hal Clement is a Grand Master of SF, and the one most associated with the subgenre of hard SF. From his classic stories in Astounding in the 1940s through his novels of the 1950s and on to the recent Half Life, he has made a lasting impression on SF readers, and on writers, too. For many of them, Clement's work is the model of how to write hard SF, and this book contains the reasons why. Here are all the tales of bizarre, unforgettable Mesklin: the classic novel Mission of Gravity and its sequel, Star Light, as well as the short stories Under and Lecture Demonstration. Also included is Whirligig World, the famous essay Clement published in Astounding in 1953. It describes the rigorous process he used to create his intriguingly plausible high-gravity planet, with its odd flattened shape, its day less than eighteen minutes long, and its many-limbed, noble natives.