The objectives of this book are set out clearly in its preface, wherein Fred Whipple states, This book tells the story, step by step, from ancient times to the present era, of our progress in understanding comets . . . The first fourteen chapters present clues and theories developed before the twentieth century; the remaining chapters provide up-to-date information regarding the nature of comets, their origin, and their possible relation to life on Earth. Comets appear to be the most primitive bodies in the Solar System and may even have played an important role in making life on Earth possible. Later chapters center on these issues, on space missions to comets, and on the general problems and significance of comets, including the hazards they may represent.