Hans A. Bethe

America is a society that encompasses and reflects the accomplish- ments of science. As civilized people, we can argue that to understand America is to und erstand the scientific genius of the men and women who built the foundations of modern science and technology. However, science is not merely a co11ection of the results of scientific research or inte11ectual wizardry. It is also a social phenomenon with real human beings with a11 their foibles. As George Sarton said, "The best way to explain American achievements is to focus the reader's attention upon a few of the leading scientists." That I have tried to do. While there are other valid approaches to the history of science, certainly the biographi- cal approach brings to ligh t the fact that science is not a mere congerie of facts and theories. It is a very human activity with biases, personal rivalries, censorship, and even thievery, as the case of Rosalind Franklin shows.

Nearly all of this book is taken from an article prepared for a volume of the Encyclopedia of Physics. This article, in turn, is partly based on Dr. Norbert Rosenzweig's translation of an older article on the same subject, written by one of us (H.A.B.) about 25 years ago for the Geiger-Scheel Handbuch der Physik. To the article written last year we have added some Addenda and Errata. These Addenda and Errata refer back to some of the 79 sections of the main text and contain some misprint corrections, additional references and some notes. The aim of this book is two-fold. First, to act as a reference work on calcu­ lations pertaining to hydrogen-like and helium-like atoms and their comparison with experiments. However, these calculations involve a vast array of approxi­mation methods, mathematical tricks and physical pictures, which are also useful in the application of quantum mechanics to other fields. In many sections we have given more general discussions of the methods and physical ideas than is necessary for the study of the H- and He-atom alone. We hope that this book will thus at least partly fulfill its second aim, namely to be of some use to graduate students who wish to learn "applied quantum mechanics". A basic knowledge of the principles of quantum mechanics, such as given in the early chapters of Schiff's or Bohm's book, is presupposed.

This book was written twenty years ago, but we are leaving it unchanged - not because little has happened to the subject, but because so much has happened that any change would require very major rewriting. On the other hand, no other book on the subject seems to have appeared and we hope this paperback edition will be of some use to a younger generation - if not for another twenty years, at least until someone else has the patience to write a new book. Although we have added no new material we have corrected some misprints. We have added new references only where they correct actual errors. We are grateful to Drs. G. Feinberg, M. Inokuti, Y. Kim, and A. Petermann for pointing out errors. Nearly all of this book is taken from an article prepared for a volume of the Encyclopedia of Physics. This article, in turn, is partly based on Dr. Norbert Rosenzweig's translation of an older article on the same subject, written by one of us (H.A.B.) about 25 years ago for the Geiger-Scheel Handbuch der Physik. To the article written last year we have added some Addenda and Errata. These Addenda and Errata refer back to some of the 79 sections of the main text and contain some misprint corrections, additional references and some notes.

Nearly all of this book is taken from an article prepared for a volume of the Encyclopedia of Physics. This article, in turn, is partly based on Dr. Norbert Rosenzweig's translation of an older article on the same subject, written by one of us (H.A.B.) about 25 years ago for the Geiger-Scheel Handbuch der Physik. To the article written last year we have added some Addenda and Errata. These Addenda and Errata refer back to some of the 79 sections of the main text and contain some misprint corrections, additional references and some notes. The aim of this book is two-fold. First, to act as a reference work on calcu­ lations pertaining to hydrogen-like and helium-like atoms and their comparison with experiments. However, these calculations involve a vast array of approxi­mation methods, mathematical tricks and physical pictures, which are also useful in the application of quantum mechanics to other fields. In many sections we have given more general discussions of the methods and physical ideas than is necessary for the study of the H- and He-atom alone. We hope that this book will thus at least partly fulfill its second aim, namely to be of some use to graduate students who wish to learn "applied quantum mechanics". A basic knowledge of the principles of quantum mechanics, such as given in the early chapters of Schiff's or Bohm's book, is presupposed.

This book was written twenty years ago, but we are leaving it unchanged - not because little has happened to the subject, but because so much has happened that any change would require very major rewriting. On the other hand, no other book on the subject seems to have appeared and we hope this paperback edition will be of some use to a younger generation - if not for another twenty years, at least until someone else has the patience to write a new book. Although we have added no new material we have corrected some misprints. We have added new references only where they correct actual errors. We are grateful to Drs. G. Feinberg, M. Inokuti, Y. Kim, and A. Petermann for pointing out errors. Nearly all of this book is taken from an article prepared for a volume of the Encyclopedia of Physics. This article, in turn, is partly based on Dr. Norbert Rosenzweig's translation of an older article on the same subject, written by one of us (H.A.B.) about 25 years ago for the Geiger-Scheel Handbuch der Physik. To the article written last year we have added some Addenda and Errata. These Addenda and Errata refer back to some of the 79 sections of the main text and contain some misprint corrections, additional references and some notes.