Branley, Franklyn M. Gravity is a mystery / Franklyn M Branley ; illustrated by Don Madden. - New York : Thomas Y. Gowell, c 1970. - 34 : ill. ; 23 cm. - Let's read and find out science books . 345 345 Subjects--Topical Terms: Gravitation--Juvenile literature.--Science Dewey Class. No.: 531.35 / B735g