The Earth: Its Origin, History and Physical Constitution, 6th edition, by Sir Harold Jeffreys
The Earth: Its Origin, History and Physical Constitution, 6th edition, by Sir Harold Jeffreys, Cambridge, Cambridge University Press, 2008, 612 pp., £35.00 (paperback), ISBN 9 780521 085182. Scope: monograph. Level: specialist.
Sir Harold Jeffreys was a leading British applied mathematician. The authorative textbook he wrote with his wife was used by generations of mathematical physicists; he made important contributions to the theory of Bayesian probability and also of quantum-mechanical tunnelling and his work on the latter problem anticipated that of Wentzel, Kramers and Brillouin (many authors refer to their result as the JWKB approximation, in recognition of Jeffreys' contribution). The main focus of his life's work was geophysics and The Earth: Its Origin, History and Physical Constitution was his majesterial treatise on the subject. It was first published in 1924 but repeatedly updated for successive editions, the sixth and final one appearing in 1976. More than 30 years later, this sixth edition has been digitally reprinted for a new audience.
Jeffreys spent his career using his formidable skill as an applied mathematician to manipulate the equations of elasticity, fluid dynamics and Newtonian mechanics to provide detailed modelling of the Earth. He was the first to show that the Earth's core must be molten, and he made important contributions to seismology, providing detailed predictions concerning the behaviour of elastic waves in the Earths's crust and outlining the theoretical principles governing how seismic data from earthquakes can be used to model the structure of the Earth. Consequently, Jeffreys' book became a standard reference work for geophysicists.
Reissuing it now has obviously been motivated by the book's status as a classic. However, a twenty-first century reader is going to encounter many problems with the text. By the time of the sixth edition, Jeffreys was in his eighties and had become a geophysical heretic (as he himself admits in one of the later chapters). He had been an early opponent of the notion of continental drift, objecting (correctly) to the notion of floating rigid continental plates driven westward by the rotation of the Earth. Unfortunately, he maintained this bitter opposition to the idea that any substantial continental movement had taken place, even as the ideas of plate tectonics were developed in the 1960s and the experimental evidence of such movements mounted, and his discussions of this topic in the book is rather grumpy and surprisingly blinkered. Jeffreys dismissed any evidence he didn't like as circumstantial or unreliable (magnetic anomalies and magnetic reversals are effortlessly disregarded on the grounds that permanent magnets are rather hard to handle, a fact the author was warned about when he ‘last did a magnetic experiment’ in ‘about 1909’). It is notable that the index of a book on the Earth contains neither the word ‘subduction’ nor the word ‘dynamo’. Even though this edition came out in 1976, reading it one has the impression that the programme of space exploration had never happened and that the only information available to an Earth scientist can be obtained from a seismograph and the solving of partial differential equations. Materials are treated elastically or as viscous liquids, and phenomena such as plasticity and transient creep, or any other unusual rheological behaviour, are largely ignored. A major part of the book contains prolonged discussion of arcane points made in research papers, the majority of which are now more than 40 years old and have surely been superceded by more recent studies and sophisticated analyses. A very large fraction of the references in the bibliography, more than 150 of them, are to Jeffreys' own work and I think this demonstrates that this text was never going to be a balanced account of geophysics of the time but was written as Jeffreys' very personal view of the subject.
In summary, I don't think that this book has stood the test of time in the way that many other classic science texts from this period (and well before) have done and I am rather surprised that it has been reissued. Diagrams are few and far between and the presentation of many of the topics (e.g. cosmology, the age of the Earth, continental drift) is very dated, even for 1976. However, Jeffreys is at his best when presenting applied mathematics, solving interesting problems and explaining theoretical approaches. On this basis, there is much to like in the book. However, for the non-expert reader who is not a geophysicist (this reviewer is in this category) but who is curious about current thinking in geophysics, it is hard to be confident how many or how few of Jeffreys' elegant applied mathematical methods reliably describe the Earth, its origin, history and constitution.
© 2010, S.J. Blundell