Among the many works devoted to our space environment, this serious and objective book by Mr. Delobeau should occupy a special place. It has become rare for works on such a subject to be written by competent physicists who are not specialists in the use of space vehicles. While performing research on the ionosphere, Mr. Delobeau was directly involved with the terrestrial environment long before it became common to explore it with sounding rockets and satellites. His professional obligations no longer require him to study aeronomy, only his regular collaboration with a great scientific journal...