In November the Geological Society of London published Volume 60 in its Memoir series, with the title The Emergence of Geophysics: A Journey into the Twentieth Century. Surprisingly, its author, Richard Howarth, is a geochemist, not a geophysicist, and, as he makes plain in his Introduction, he was led into writing the book by his interest in mathematical methods in the Earth Sciences. Geophysics, however, is much more than mathematics, as is abundantly recognised in the book itself. According to the description supplied by the Society, it deals with the questions:
How did geophysics begin? Who were the pioneers of this new science? What instruments did they devise to measure the Earth-related phenomena they were interested in? This Memoir attempts to answer such questions in a well-illustrated, and largely non-technical, account.
And notes that
“The seventeenth century saw magnetism used as an aid to prospecting for iron ore in Sweden, and Isaac Newton’s derivation of the law of gravitational attraction. A gradually increasing interest in ‘physics of the Earth’ brought forth the new discipline of ‘geophysics’ in the early nineteenth century and, by the end of the following century, airborne and satellite-based investigations had become routine. The Emergence of Geophysics explores this evolution in several parallel strands: terrestrial magnetism and electricity, gravity, seismicity, heat, geodynamics and radioactivity, broadly reflecting the timing of their introduction as tools aiding geophysical studies. Biographical information is included for many of its practitioners and the book should be of interest to both geophysicists and to anyone interested in the history of Earth science.”
Electrical prospecting in Cornwall in 1905. The cover illustration to The Emergence of Geophysics. Credit: Robert Vernon and the Williams family.
One might quarrel with Newton as the starting point, and indeed one could argue that, far from physics having given rise to geophysics, physics itself owes its origin to geophysics and its sister science of astronomy. William Gilbert published his groundbreaking De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth) in 1600, and well before that Galileo had completed his first series of experiments with gravity, without which Newton would have been helpless, even if apple-assisted.
Howarth, however, is presumably not responsible for what the Society has to say about his book, because in it neither Gilbert nor, to a lesser extent, Galileo is ignored. He had a much more difficult decision to make than deciding the point in time at which he should begin, in deciding the point at which he should end, because the word ‘emergence’ in the title implies that its readers will not be carried all the way to the present day. He is very definite in his Introduction. He will consider developments as far as the end of the 20th century but will not venture into the 21st.
Is this the best choice, and does Howarth actually respect his own self-imposed limitation? I have my doubts in both respects. The arbitrary turn of the century has no special place in the evolution of the science, and the actual implementation of the cut-off in the book is not entirely consistent, as is evident where the Introduction deals with geophysical journals. The journal ‘Geophysics’, first published in 1936, is mentioned only in a listing in which it is the last but one entry (the Italian Geofisica Pura e Applicata, first published in 1939, is the last) and Geophysical Prospection, which first appeared in 1962, is not even mentioned. However, rather than criticising the omission of journals post-1939, I would suggest that in doing this Howarth has selected a far better cut-off point for what he set out to do, and that he should very definitely not have succumbed to the temptation to extend his scope, as he does in some cases, into the 21st century. It is simply not possible to describe in a single volume the explosive growth in geophysics that occurred in the second half of the 20th century in the sort of detail he devotes to developments in some aspects of geophysics prior to the first appearance of Geofisica Pura e Applicata, and I personally think that it was a mistake even to try.
In what respect was 1939 a turning point? Most obviously, it marked the beginning of the Second World War, during which there were multiple developments in a science that had not, up to then, been very different from the physics of the laboratory. It is true that the observations were in most cases made in ‘the field’ rather than within the controlled environments of laboratories, but few of the instruments used would have seemed out of place in laboratory settings. Magnetometers, gravity sensors, seismometers and potentiometers were read in discrete locations, and were calibrated, adjusted and oriented as they would have been in laboratories. The compromises that were forced on their users by the need to move them around in sometimes hostile environments set the scene for what was to come, but it was war that accelerated the introduction of two factors that, although they revolutionised the science, were not in themselves scientific: mobility and the application of multiple methods in the approach to a single problem. Just one final chapter foreshadowing those developments would have made for a tidier book.
It would also, if that only were done, have been a significantly shorter one, and considering the bulk and weight of its 438 pages, that might have been welcomed by its readers (to whom I would recommend downloading, for free, the online version). Some might also question, as I would, whether topics as complex and wide-ranging in their own right as solar physics, volcanology, geodynamics (which overlaps into other chapters) and radiometric dating really have a place in it, in such necessarily abbreviated forms. More rigorous pruning in subject matter as well as in time would have allowed deeper consideration of some things that are, to working geophysicists, rather fundamental. I searched in vain, in the longest chapter of all (the second of the two on terrestrial magnetism) for any mention of the differences, operationally and in interpretation, between measurements of total and component (usually vertical) magnetic fields, in the chapters on both electrical and seismic methods for any discussions of the ways in which the initial signals were produced that would match the discussions of the ways in which they were detected and, in seismic methods, of the all-important matter of the frequency content of artificially-generated seismic waves. These are all topics that cry out for informative diagrams, and although the book is copiously illustrated, those necessary illustrations are lacking.
Nor is the treatment even-handed between methods. History, the saying goes, is about chaps, and in dealing with magnetics (the only topic allotted two chapters, which together occupy a quarter of the book), the work of several of the early ‘chaps’, and the obstacles, personal and physical, that they had to overcome to get their data, are described in loving detail. The multi-page treatment of the (undoubtedly significant) work done by Edmond Halley is in stark contrast to the treatment of Andrija Mohorovičić, the first man to identify the interface between the crust and the mantle. To do this he used measurements of seismic wave arrival times from not only his own seismometers but from dozens of others scattered around Europe, but while several copiously illustrated pages are devoted to the instruments in use at the time, who Mohorovičić was and what he did are summarised together in a single paragraph. The lives of 20th century scientists are generally given only in their bare essentials except, again, in magnetics. Its role in the development of plate tectonics is treated a little more expansively, and regarding the rejection of the paper by Lawrence Morley that first provided an explanation of oceanic magnetic anomalies, the discussion includes the mysterious comment that ‘it may have been …… reviewed by someone from Cambridge’.
These are the shortcomings of the book, as I see them, but in identifying them I am very far from wishing to detract from its obvious merits. It is almost inevitable that any geophysicists reading it will find grounds for complaint in what they will see as the inadequate treatment of their own pet topics or obsessions, but those well probably be different from mine. The book is a massive achievement and the pre-1939 developments, which make up its bulk, are invaluably referenced even where they are not fully discussed. Those reference listings alone occupy almost a hundred pages.