The development of numerical integration techniques and the pioneering efforts of Von Neumann and his associates at the Institute for Advanced Studies (Princeton) have spurred the renewed interest of many leading fluid dynamicists and meteorologists in the theory and numerical simulation of planetary atmosphere and oceans circulations. Their work during the last 15 years, now culminating in the Global Atmospheric Research Program, has led to the possibility of vastly improved weather forecasts as wei I as the development of a ful I fledged branch of the physical sciences: geophysical fluid dynamics. Simultaneously, great strides have been made in developing new instruments, operating from earth orbiting satel I ites, to powerful observe the meteorological phenomena and to determine the state of motion of the atmosphere. Centre National d'Etudes Spatiales (CNES) of France has very significantly contributed to this effort by developing the EOLE navigation and data collection satell ite, launched on 16 August 1971 to interrogate 500 instrumented platforms measuring meteorological para meters. It is fitting then, that CNES should have brought together lead ing scientists in the field of dynamic meteorology, to participate in its 1970 Summer School on Space Physics."

The development of numerical integration techniques and the pioneering efforts of Von Neumann and his associates at the Institute for Advanced Studies (Princeton) have spurred the renewed interest of many leading fluid dynamicists and meteorologists in the theory and numerical simulation of planetary atmosphere and oceans circulations. Their work during the last 15 years, now culminating in the Global Atmospheric Research Program, has led to the possibility of vastly improved weather forecasts as wei I as the development of a ful I fledged branch of the physical sciences: geophysical fluid dynamics. Simultaneously, great strides have been made in developing new instruments, operating from earth orbiting satel I ites, to powerful observe the meteorological phenomena and to determine the state of motion of the atmosphere. Centre National d'Etudes Spatiales (CNES) of France has very significantly contributed to this effort by developing the EOLE navigation and data collection satell ite, launched on 16 August 1971 to interrogate 500 instrumented platforms measuring meteorological para meters. It is fitting then, that CNES should have brought together lead ing scientists in the field of dynamic meteorology, to participate in its 1970 Summer School on Space Physics.

My colleagues and I have been gratified by how rapidly the first edition of Myelin has been aeeepted as a standard referenee work by myelin researehers. This is undoubtedly the primary faetor aecounting for the high rate of reeidivism among the authors with respeet to preparation of a seeond edition; eleven of the original twelve contributors were again involved. Four new authors (Wendy Cammer, Marjorie Lees, Ute Traugott, and Seymour Greenfield) have also eontributed to the present volume. This new edition retains many aspects of the format of the original, even including use of the same chapter headings. Thus, comments in the preface to the first edition concerning the level at which material is presented and the relationships between chapters covering the "basic" and "c1inical" material are still applicable. Despite certain similarities in overall organization, comparison of the present edition with the original demonstrates that our eHorts to restriet expansion in the length of the text were not notably successful; the new edition is mueh lengthier than the original. Nevertheless, the increase in text length is modest relative to the increase in information in the seven years separating the preparation of the two editions. Most of the material in the individual chapters has had to be completely redone in order to include this new information. For example, our view of the metabolism of myelin increasingly must take cognizance of a very rapidly turning over pool of certain of its components.