The Doubleday hardcover was in 1954; this is the first mass-market American paperback edition. (Also as GALAXY Novel #33 - 1958.)

Hal Clement's most famous novel: Mission of Gravity. The planet Mesklin is massive- gravity varies from 3G at the equator to 700G at the poles. Humans, having crashed a probe at the poles, hire a native seacaptain (Barlennan) to recover their probe. The humans with their higher technology think they're in charge, but Barlennan has some plans of his own...