and by the Librarians and Staffs ofthe University and the Public Libraries at Southampton. Finally, we wish to thank Mrs H. G. Jerrard and Miss A. J. Tutte for typing the manuscript. Department of Physics H. G. JERRARD University of Southampton D. B. McNEILL 1963 Preface to the fifth edition Since the publication of the fourth edition in 1980 advances in technology have led to more precise values of the fundamental physical constants and a movement towards definitions of the fundamental units of mass, length and time based on atomic parameters. More precise definitions of some other units such as the candela have been approved by the international committees. These changes, together with the definitions of several new units have been included in this edition, the text of which has been revised and which now contains over 850 units and dimensionless numbers. The authors wish to thank all those who have helped in this latest compilation by suggestion and kindly criticism and Margaret Wainwright who has had the difficult and tedious task of typing, retyping and copying the fragmented parts that arise from a text revision. At the time of going to press we believe this book to provide the most complete and up-to-date information of its kind available.

units have been included. References, which now number approximately 650, have been brought up to date. The most recently accepted values of the physical constants have been provided. Our thanks go to all those who, since the fifth edition, have helped in this revision by suggestions. In particular the authors express their gratitude to Jane M. Jerrard who, with enthusiasm, put the text into a computer and eliminated the editorial scissors and paste and simplified the onerous and long task of producing a text from the fragmented material of the revision. In the preface to the fifth edition it was suggested that the book provided at that time the most complete and up-to-date information of its kind available. The authors again make the same claim for this sixth edition. H. G. JERRARD D. B. McNEILL Warsash Newtownards Southampton Northern Ireland England Preface to the first edition The intense specialization that occurs in science today has meant that scientists working in one field are often not familiar with the nomenclature used by their colleagues in other fields. This is particularly so in physics. This dictionary is designed to help overcome this difficulty by giving information about the units, dimensionless numbers and scales which have been used, or are still being used, throughout the world. Some four hundred entries are provided and these are supplemented by about five hundred references. The definition of each entry is given together with relevant historical facts.

and by the Librarians and Staffs of the University and the Public Libraries at Southampton. Finally, we wish to thank Mrs H. G. Jerrard and Miss A. J. Tutte for typing the manuscript. Department of Physics H. G. JERRARD D. B. McNEILL University of Southampton 1963 Preface to the fifth ed ition Since the publication of the fourth edition in 1980 advances in technology have led to more precise values of the fundamental physical constants and a movement towards definitions of the fundamental units of mass, length and time based on atomic parameters. More precise definitions of some other units such as the candela have been approved by the international committees. These changes, together with the definitions of several new units have been included in this edition, the text of which has been revised and which now contains over 850 units and dimensionless numbers. The authors wish to thank all those who have helped in this latest compilation by suggestion and kindly criticism and Margaret Wainwright who has had the difficult and tedious task oftyping, retyping and copying the fragmented parts that arise from a text revision. At the time of going to press we believe this book to provide the most complete and up-to-date information of its kind available.