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 inspires him to keep up to date on this subject. He is particularly motiva ted by a disinterested appreciation of the information which he hopes to share with his readers. It is a sign of the times that the results of space research should no longer be confined to the circle of space technicians. All of the new tools available to the service of science, for example:-particle accelerators, magnetic resonance, electron microscopy, lasers - have entered the general arsenal following a period of adaptation. Like them, the rocket is now a classical instrument, and gives information even to those for whom it holds no interest in itself. This book was quite up-to-date when the author submitted his manuscript. Despite the efforts of the editor, this will no longer be completely true when it appears in print. There is scarcely any branch of science that evolves more rapidly than space research.

Inhalt
I. The Earth in Space.- 1. Introduction.- 2. Historical Survey.- 3. The Structure of the Atmosphere.- 4. The Neutral Gas.- A. Composition.- B. Temperature.- C. Pressure and Density.- 5. The Ionized Gas.- 6. The Van Allen Belts.- 7. The Frontier.- II. The Terrestrial Magnetic Field.- 1. Description of the Earth's Magnetic Field.- A. Study of the Magnetic Field.- B. Geometry of the Magnetic Field.- 2. Electrically Charged Particles and the Magnetic Field.- A. Cyclotron Motion.- B. Particle Drift.- C. Behavior in the Real Magnetic Field.- D. Störnier: A Precursor.- 3. Electromagnetic Waves in an Ionized Medium and in the Presence of the Earth's Magnetic Field.- A. The Collisionless Medium.- B. The Medium with Collisions.- C. The Real Case.- D. The Whistler Mode.- E. Hydromagnetic Waves.- III. The Terrestrial Ionosphere.- 1. Solar Radiation.- A. The Sun and its Luminous Radiation.- B. The Solar Cycle.- C. Atmospheric Absorption.- 2. Formation of the Ionosphere.- 3. The Lower Ionosphere.- A. The D Region.- B. The E Region.- 4. The High Ionosphere.- A. The F1 Layer.- B. The Lower F2 Layer.- 5. Dynamics of the Ionosphere.- A. Motions of the Neutral Atmosphere.- B. Motions of the Ionized Atmosphere.- IV. The Outer Ionosphere and the Van Allen Belts.- 1. General Considerations.- 2. The Exosphere and the Upper Ionosphere.- A. Neutral Particles.- B. Thermalized Charged Particles.- 3. The Van Allen Belts.- A. Discovery of the Belts.- B. The Inner Belt.- C. The Outer Belt.- D. Artificial Belts.- V. The Borders of the Terrestrial Environment.- 1. Introduction.- 2. The Solar Wind and the Interplanetary Magnetic Field.- 3. The Magnetopause.- 4. The Shock Front.- 5. The Earth's Magnetic Tail.- VI. Disturbances in the Atmosphere.- 1. Electromagnetic Emission from the Active Sun and Sudden Ionospheric Disturbances.- A. Solar Flares.- B. Ionospheric Disturbances.- 2. Corpuscular Emission from the Active Sun.- 3. Solar Cosmic Rays and Polar Cap Absorption.- A. Solar Cosmic Rays.- B. Polar Cap Absorption in the Ionosphere.- 4. Magnetic and Ionospheric Storms.- A. Magnetic Activity.- B. Development of a Magnetic Storm.- C. The Ionospheric Storm.- 5. Polar Aurorae.- 6. Theory of Storms and Aurorae.- A. Statement of the Problem.- B. The Theory of Axford and Hines.- C. Geophysical Consequences.- VII. Micrometeorites.- 1. Micrometeorites and Their Detection.- 2. Meteoritic Astronomy.- 3. The Direct Study of Micrometeorites.- 4. Origin of the Micrometeorites.