Man's view of the universe is widening today, as it did once before in the early days of big telescopes and photographic plates. Modern man, by means of radio, infrared, optical, ultraviolet, and X-ray astronomy, can penetrate the universe to depths never before explored. Phillip James Edwin Peebles has written a pioneering work in this newly defined area of investigation. Intended to bridge the chasm between classical textbooks on cosmology and modern developments, serves as a guide to current points of debate in a rapidly changing field. Originally published in 1972. The uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.