J. A. Jacobs – författare

By measuring the direction and intensity of magnetism in rocks of different ages, a record of the Earth's magnetic field in the past can be obtained. This 1994 book deals with the particular case of reversals of the Earth's magnetic field. These have played a major role in the development of plate tectonics and in establishing a geological time scale. The magnetism of rocks is discussed in some detail with a warning of possible misinterpretations of the record. Observational results and theories are reviewed with special attention to the structure and geometry of the transition field. Changing conditions at the core-mantle boundary, their effect on reversals, the generation of plumes and the possible correlation of reversals with tectonic changes, ice ages or mass extinctions are thoroughly discussed, including suggested periodicities in the reversal record and in other geophysical data.

By measuring the direction and intensity of magnetism in rocks of different ages, a record of the Earth's magnetic field in the past can be obtained. This 1994 book deals with the particular case of reversals of the Earth's magnetic field. These have played a major role in the development of plate tectonics and in establishing a geological time scale. The magnetism of rocks is discussed in some detail with a warning of possible misinterpretations of the record. Observational results and theories are reviewed with special attention to the structure and geometry of the transition field. Changing conditions at the core-mantle boundary, their effect on reversals, the generation of plumes and the possible correlation of reversals with tectonic changes, ice ages or mass extinctions are thoroughly discussed, including suggested periodicities in the reversal record and in other geophysical data.

The Earth''s Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth''s crust; interpretation of gravity anomalies; and gravity anomalies and the interior of the earth. Topics include general principle; direct and indirect methods; low order harmonics in the gravitational field; rock densities; ocean trenches; and sedimentary basins. The book then examines the place of gravity measurements in geophysical prospecting and tidal variations of gravity. The manuscript is a dependable source of information for readers interested in the shape and gravity of the earth.

The Physics of Ice covers the state of knowledge regarding the structure, properties, occurrence, and movement of ice. This book is composed of eight chapters, and begins with an introduction and in the fundamental aspects of ice, including pure water freezing, circulation, occurrence, classification, and importance of ice. The subsequent chapters describe the properties, structure, freezing, and composition of sea ice and ice drift. These topics are followed by discussions on the crystallographic features, and mechanical, thermal, and electrical properties of ice. The concluding chapter examines the factor influencing ice growth and decay. This book is directed toward physicists and researchers in ice-related fields.

An account of some aspects of marine geology and marine geophysics, comprehensible to those at an early stage in their study of geology and to scientists who are not specialists in these fields. There are many biologists, chemists, mathematicians or physicists who work in the laboratory or on board ship with geologists and geophysicists and this book will help them to understand the aims of their colleages'' experiments. Wherever possible, without a loss of necessary precision, terminology is deliberately simplified.

The subject of geomagnetic micropulsations has developed extremely rapidly and it is difficult to know when is an appropriate time to pause and assess the sum total of our knowledge-both observational and theoretical. There has in recent years been a tremendous increase in both the quantity and quality of data and also many theoretical ad­ vances in our understanding of the phenomenon. Undoubtedly there will be further progress in both areas but it seems worthwhile now to review both our knowledge and our ignorance. This book was essen­ tially completed by the end of April 1969 and tries to give a summary of the subject up to that time. The Earth is enclosed in the magnetosphere, a hollow carved out of the solar wind by the Earth''s magnetic field. Above the ionosphere there is a very tenuous thermal plasma of partially ionized hydrogen in diffusive equilibrium with magnetic and gravitational forces, and ener­ getic protons and electrons that constitute the trapped Van Allen ra­ diation belts. Throughout this anisotropic and inhomogeneous plasma, natural and man-made electromagnetic energy propagates in a wide variety of modes and frequency bands. This book is concerned with that class of natural signals called geomagnetic micropulsations-short period (usually of the order of seconds or minutes) fluctuations of the Earth''s magnetic field.