Almost every geodetic measurement depends in a fundamental way on the earth’s gravity field. Therefore, the study of the physical properties of the gravity field and their geodetic application, which are the subject of physical geodesy, forms an essential part of the geodesist’s education. During the ten years that have passed since the writing of The Earth and Its Gravity Field by Heiskanen and Vening Meinesz, geodesy has progressed enormously. To incorporate the results of this progress, which has been theoretical as well as practical, in a new edition of that book became increasingly impossible. It was necessary to write an entirely new textbook, one that is different in both scope and treatment. The great increase in the amount of available information required a strict limitation to geodetic aspects; advances in theory made neccssary an increased emphasis on mathematical methods. The outcome is the present book, which is intended to be theoretical in the sense in which the word is used in the term “theoretical physics.” This textbook, intended for graduate students, presupposes the background in mathematics and physics required by geodesy departments of American and European Universities. The necessary fundamentals of potential theory are presented in an introductory chapter. Chapters 1 through 5 cover the material for a basic course in physical geodesy. Chapters 6 through 8 present a number of more specialized and advanced topics, where current research activity is high. (These chapters are likely to be more subjectively biased than the others.) The reader who has mastered them should be able to begin research of his own. For the sake of completeness we have added a chapter on celestial methods; this material may be included in the basic course. We have tried hard to make the book sclf-contained. Detailed derivations are given wherever feasible. Our approach is intuitive: verba! explanations of the principles were felt to be more important than formal mathematical rigor, although the latter is not ignored. Our general attitude is conservative. We do not believe that the concept of the geoid has become obsolete. This docs not mean, however, that we are unaware of the great significance of recent theoretical developments associated mainly with the name of Molodensky: we discuss them in Chapter 8. Observational techniques such as those used in gravity measurements or astronomical observations are deliberately omitted as being out of place in a theoretically oriented presentation. Bibliographies of works cited in the text, many of which should be useful for further study, will be found at the end of each chapter; citation in the text is by author’s name and year of publication—for example, Kellogg (1929). We have not attempted to settle questions of priority. Names associated with formulas should be considered primarily as convenient labels. Similarly, the most readily accessible or most comprehensive publication of an author on a particular topic is given rather than his first. Most of our own research incorporated in this book has been done at The Ohio State University. We wish to thank Dr. Waiter D. Lambert for carefully checking parts of the manuscript for correct English.
