Typical of the author's "Exploring" books, [Man's Reach into Space] is … well written and full of information…. It is longer than the others, and more unusual in that it deals with a new subject—the gaining of knowledge that will help us to send men safely out into space. What can the human body endure in the way of unearthly environments, sudden extreme decelerations, exposure to heat or to low air pressure, or just to endless boredom and enclosure? I have seen no discussion of the human side of space flight, written for any age level, that is as interesting and informative as this.
Isaac Asimov, "Early Spring Booklist: 'Man's Reach into Space'," in The Horn Book Magazine (copyright, 1960, by the Horn Book, Inc., Boston), Vol. XXXVI, No. 2, April, 1960, p. 146.
[Exploring Under the Earth] is the story of geology and geophysics, and covers a range that is perhaps beyond what one might expect. [Roy A. Gallant] goes back to the formation of the earth, the atmosphere, the oceans; then on to the development of geology as a science. The new findings of the under-ocean world are given their place; the formation of continents, the facts about earthquakes, about volcanoes, the building of mountains, the significance of magnetism and the poles—all this is brought together in readable, concise form.
"Non-Fiction: 'Exploring Under the Earth'," in Virginia Kirkus' Service, Vol. XXVIII, No. 22, November 15, 1960, p. 962.