[The Earth: Planet Number Three is a] stimulating account of man's present knowledge of planet Earth. The author considers three large topics: the atmosphere, sea, and land. He explores theories concerning the origin and age of the earth and tells how scientists study the motion, size, and shape of the planet, and how they probe the problems of gravity, geomagnetism, radiation belts, etc. At times the text is difficult, but the careful presentation of the subject matter, within historical perspective, brings to the reader a sense of excitement and wonder at man's endeavor to learn more about the universe. (pp. 160-61)