The invisible intangibles are the most difficult to present to young readers, but Mr. Hicks' blend of example, anecdote and fact explores the knowns and the unknowns of the atmosphere with a crisp brevity well suited to this age level's attention span. From the polluted layers of air surrounding the earth (we are the ""first creatures in history to poison the world in which we live"") to the mystifying ""messages"" picked up by radio telescope from the farthest reaches of our galaxy, this is a thorough and well organized briefing on the physical nature of the strata of atmosphere and the potential use to which present knowledge will be put in the conquest of outer space. A rundown on research in progress is included.