A matter of gravity: the emergence of geophysics as a separate discipline
|From: Wilson, H.E. Down to earth - one hundred and fifty years of the British Geological Survey. Edinburgh:Scottish Academic Press, 1985.|
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XIII A matter of gravity: the emergence of geophysics as a separate discipline
In 1774 Nevil Maskelyne, the Astronomer Royal, carried out an experiment near Schiehallion, a mountain in northern Perthshire, to 'determine the attraction of mountains by deviation of the plumbline'. From his results the density of the earth was estimated to be 4.5, perhaps the earliest geophysical calculation.
In 1811, some doubts having been cast on Maskelyne's work, the Board of Ordnance asked John McCullough who had held a part-time appointment as a chemist for eight years, to look for an area more suitable than Schiehallion to repeat the experiments and the earliest official geological/geophysical work in Britain began. It was to be a century before there was any further interest in geophysics from McCullough's successors, the Geological Survey.
In 1917, in conjunction with the Iron Ore Committee of the Conjoint Scientific Societies, an investigation of the magnetic anomalies in the Jurassic areas of Leicestershire was carried out by A H Cox with somewhat inconclusive results.
In the mid-twenties the Geological Survey Board included Sir John Cadman, Chairman of the Anglo-Iranian Oil Co, and he encouraged the investigation of geophysics as an aid to normal survey methods. In 1926 the Company invited the Survey to send two geologists to Iran (then called Persia) to see how they were using the Eatviis torsion balance — the first practical instrument for detecting gravity anomalies. The chosen pair were McClintock, the curator of the Museum, and Phemister, the petrographer from the Edinburgh office, who travelled by way of Marseilles, P & 0 ship to Port Said and Anglo-Iranian tanker to Abadan, the journey taking 20 days. They spent two months with the oil company geophysicists and reported so favourably on the results achieved that the Survey bought an aitvos balance in 1926 and McClintock and Phemister carried out a series of trials in Britain with this new toy — tracking a basalt dyke in Staffordshire in 1927, delineating the drift-filled pre-glacial channel of the River Kelvin in 1928, locating the Pentland fault in 1929, and following up magnetic anomalies in Leicestershire in 1930. Helping in the last was a young geologist called Mourant who recalls the physical effort involved — the Eotvos balance weighed nearly a hundredweight. Mourant, who was regarded as unsuitable by Flett, the Director, left the Survey shortly afterwards, but went on to become an authority on blood grouping and a Fellow of the Royal Society.
Concurrently with the experimental gravity work, A F Hallimond, Assistant Curator of the Museum, undertook a series of trials with a portable magnetometer — it is curious that almost all these early workers were museum or specialist staff. With the exception of Mourant, the subject was presumably deemed too esoteric for field geologists. Hallimond — who for many years acted as a consultant on the design of petrological microscopes — carried out a parallel series of observation on the Staffordshire dyke, the Pentland Fault and Leicestershire. Though these early efforts showed the promise of its future application the geophysical programme was suspended in 1931 and all the instruments lent, for teaching purposes, to Imperial College. Bailey, writing fourteen years later, suggests that this was due to the influence of the new Chairman of the Survey Board, Dr T Franklin Sidly.
In 1938, however, following the work of a university lecturer, J T Whetton, on the Cumberland haematites, Hallimond took a magnetometer to Cumbria and his results, with those of Whetton, were published in the second Bulletin of the Geological Survey. This was the last geophysical work carried out before World War II.
One of the first post-war recruits to the Survey was William Bullerwell, a double graduate in physics and geology, who after a short period as a field geologist was given by McClintock, by then Director, the task of reviving the geophysical work of the Survey, in 1947.
His first job was to reassemble the equipment which had been on loan to Imperial College for sixteen years, and to take it in the field. The elderly Eotvos Torsion Balance was used in an area in north Cheshire where a survey with more modern equipment had been made by the Anglo-American Oil Co. As the report of the Survey Board put it — 'The work shows the value of combining the technique of torsion balance with that of the gravimeter, an instrument which it is hoped to acquire for the Geological Survey in the near future'.
After a last fling — struggle would be a better word — with the Eötvös in the Bristol coalfield in 1948, a Frost gravimeter was obtained and for the next five years most of Bullerwell's time was taken up with gravity work, particularly since, in 1950, the Survey had undertaken the collection and collation of all gravity data acquired in Britain by university workers and commercial (mainly oil company) operators.
By 1951 work by the Geophysical Department — it was so called after 1950 — had linked all the main independent gravity surveys in the UK, and in 1952 the network was extended to include Ireland, with a Worden gravimeter being flown on commercial flights from Manchester to Belfast and Dublin.
In 1953 the first seismic equipment was brought into use and was used for investigations in Sussex. In the same year resistivity surveys were undertaken for the first time, so it must have been a relief to Bullerwell when the first graduate geophysicist joined his unit in 1954, all his assistants till this time having been Experimental Officers. In 1956 the first quarter-inch to one mile (approx. 1:250 000) geophysical map was published — a transparent overlay showing Bouger gravity anomalies in the south midlands of England — and the first gear for electrical logging of boreholes was obtained as 'economic aid' from the USA under the 'Marshall Plan', the generous scheme for the economic rehabilitation of Europe after World War II.
For the next decade gravity and magnetic surveys to complete the coverage of the United Kingdom were steadily pressed forward, the main development being the use of airborne magnetic surveys flown by outside contractors. The impetus to use these modern techniques came, not from DSIR, but from the Nuffield Foundation who financed the first work in 1956. When the enormous advantages in speed and completeness of airborne magnetic surveys became obvious DSIR was persuaded to pick up the bill.
In 1966 the Geophysical Department took to the sea, using a marine proton magnetometer to investigate an anomaly in Loch Ewe and a sonic and magnetic package to carry out an extensive survey of the Moray Firth. To complete the metamorphosis to marine activities the unit participated in a joint university project which covered areas of the Continental Shelf south and west of Ireland. In the same year the first crustal seismic experiments were undertaken using massive marine explosions recorded by land-based seismometers.
The amalgamation of the home and Overseas Geological Surveys in 1966, and subsequent developments, made a profound difference to the Geophysical Department. A home-based Geophysical Section of Overseas Surveys had existed since 1955, working with and advising the colonial surveys in many parts of the world. This well-equipped unit was rapidly amalgamated with the home personnel and by 1967 was described as the applied geophysics group of three Applied Geophysics Units, working on ground and airborne geophysical surveys in Britain; regional surveys and prospecting for water and minerals overseas; and marine surveys in the Irish Sea.
In the same year NERC assumed responsibility for geophysical work in two fields which had long been studied by other departments — geomagnetism and global seismology. The former had been under the control of the Royal Greenwich Observatory at Herstmonceux in Sussex and Hartland Point in Devon and at Eskdalemuir and Lerwick in Scotland, where it was administered by the Meteorological Office. The latter, also a Meteorological Office responsibility, was based at Eskdalemuir and Edinburgh and was in co-operation with the Royal Observatory, Edinburgh.
Naturally the assimilation of these diverse organisations took some time, and it was 1969 before transfer to IGS was complete.
The new Geomagnetism Unit had an interesting history and can, indeed, claim to have preceded the Geological Survey by six years, in that systematic observations of the earth's magnetic field were started by Airy, the Astronomer Royal, in 1829. Indeed Halley made magnetic surveys at sea in 1701 and Flamsteed measured Magnetic Declination in 1680!
Regular observations of magnetic values started with the assistance of the Hydrographer of the Admiralty to help the calibration of ships' compasses and, in 1818, a 'Magnetic House' was built in the garden of Greenwich Observatory. In 1836 Airy, just appointed Astronomer Royal, was asked to comment to the Royal Society on proposals from von Humboldt in Berlin that magnetic observatories should be set up throughout the world with the help of European Scientific Societies. Starting the expansionist tradition followed by virtually all heads of scientific organisations since, Airy agreed enthusiastically with a proposal which might enlarge his establishment and a new building was completed in 1838 for the purpose. Admiralty requirements for studies on the effects of iron ships on compasses, and the Royal Society needs for magnetic observations in connection with the Antarctic expedition of Sir James Clark Ross, ensured adequate support and from that time observations of meteorological and magnetic instruments were made every two hours on every day except Sunday, Christmas Day and Good Friday!
For ten years the Superintendent and his two assistants worked a shift system to make these readings, recording the time on a watchman's clock to allow Airy to check the punctuality of the observations. Though photographic recording equipment ended night-shift observations in 1847 — only six years after Fox Talbot patented his Calotype process — the watchman's clock continued in use till the 1940s and Dick Leaton, the last Superintendent, recalls a watchman of that era who told him 'that the clock could be deceived'. Perhaps Airy's confidence was misplaced — but as an example of practical application of a new invention the recording gear devised by Charles Brooke in 1847 puts twentieth-century British industry to shame!
Magnetic observations continued at various sites in the Greenwich park till 1924 when interference from the new Southern Electric Railways caused the magnetic observatory to be moved to Abinger, about 30 miles SW of Greenwich, though here too the dread Southern Electric soon made its presence felt. Finally, after World War H, it was decided to seek a site at least ten miles from the nearest railway and in 1956 a new observatory was opened at Hartland Point in north Devon, which is notable not only for the lack of railways but also of roads more than 3 m wide! This station passed from the Science Research Council to NERC in 1967, with the other staff from Herstmonceux, whence the Greenwich Observatory had moved in the late 1940s.
For the next decade the Unit continued in its existing accommodation — the headquaters at Herstomonceux and outposts at Hartland, Eskdalemuir and Lerwick, with an office in St. Oswalds Road in Edinburgh, shared with the Global Seismology Unit. In 1977, with the opening of Murchison House, the Herstmonceux headquarters was moved to Edinburgh and the St. Oswalds Road Office was closed.
The work of the Geomagnetism Unit is basically concerned with the strength and variation of the earth's magnetic field, which is approximately the same as would be produced by a bar magnet aligned from pole to pole. There is evidence that the movements in the electrically conducting core of the earth cause deviations of the field from the simple bar magnet pattern and one of the main tasks of the Unit is the compilation of world magnetic charts for the use of navigators; and research into the origins of variations in the field, caused by slow processes in the earth's core or by solar events. Short-term variations, lasting from a few hours to a day or more, are known as magnetic storms which can arise quite suddenly, without warning, and are connected with events taking place on the sun notably sunspots. They often occur on a 27-day cycle — the period of solar rotation. These solar events cause fluctuations in the discharge of charged particles from the sun — the solar wind — and this affects the Earth's magnetic field. The study of these events, their effect on navigation and telecommunications and the interpretation of the results in terms of the deep structure of the earth and the effects on the ionosphere are the remit of the Geomagnetism Unit — a blend of pure and applied science which unhappily has come to be regarded as not 'economic' in Rothschild terms.
The Global Seismology Unit resulted from the decision to rationalise government support for seismological research in Britain, which up to the mid-60s had been in three parts: the NERC-supported Seismological Unit in Edinburgh University, which included an International Seismological Centre supported by international funds; the Seismological Unit of the Royal Observatory in Edinburgh funded by Science Research Council; and the seismological work at the Eskdalemuir observatory, originally directed to the seismological detection of atomic weapon testing, which had been administered by the Meteorological Office.
The amalgamation of the first two was accomplished with the formation of Global Seismology Unit in 1967 under the leadership of Dr P L Willmore, who remained Director of the International Seismological Centre. At that time the Royal Observatory had developed programmes for the computer processing of the vast amounts of information becoming available from automatic seismic recording while the Seismological Centre had extensive research operations ongoing in Sicily and Brazil, and was developing a study in Scotland — the Lowlands Network (LOWNET) based on portable seismometers with radio-telegraphy links to a central processor.
In 1968 the Eskdalemuir observatory was merged with Global Seismology Unit and since then work has spread across a broad front of seismological research. The development of portable telemetric instruments has continued and work has been undertaken in seismic areas — Iran, Turkey, Brazil, Panama — as well as in the UK. The Unit has been fortunate in that, up to 1983 at least it had been able to resist commissioned research outside its selected research areas, but pressure to seek any contract which will generate money is growing.
Up to the present the main research areas of GSU have been under four heads. First, and the most productive of outside funds, has been the investigation of British earthquakes, using a nationwide network of seismographs. Earth tremors in Britain are infrequent and often due to mining activity — or quarry blasts and sonic booms — but occasional events, such as that on Boxing Day 1979 in SW Scotland, cause public concern and a media focus on the Unit, whose Christmas holiday was notably interrupted on that day. Their widely-distributed questionnaire asking for details of local effects produced, at least on that occasion, a number of somewhat bawdy public parodies! Questions eleven and twelve particularly, offered scope to the humorists — 'Did anything else rattle?' and 'Did any hanging objects swing?'.
The other main subjects of research include the study of wave propagation in cracked and anisotropic solids and its application to earthquake processes and seismotectonics: seismic hazard research including work in the Volos area of mainland Greece in association with the Engineering Geology Unit and Greek organisations: instrument development, following the very successful portable seismometer development led by Willmore in the 1960s.
From 1967 therefore the erstwhile Geophysical Department with four scientific officer staff became the Geophysical Division, with three units and a scientific officer staff of 18, plus about 30 support staff, and Bill Bullerwell entered the IGS hierarchy of which he was soon to become the lynch-pin. In the same year a new unit was added to the Division — the Engineering Geology Unit, set up in the first instance to measure the physical properties of rocks to supplement the work of other units in the division, and in 1968 the Marine Geophysics Unit was formed in response to the rapid growth of offshore work, while home and overseas work on land was the responsibility of the Applied Geophysics Unit.
The division was still small — the new units had only two or three men — in 1970, when it received its final accession — the Blacknest Group. At this time it had a scientific officer strength of about 25, with 50 experimental officers and technicians in support.
The Blacknest Group was, when it joined IGS, a two-man team led by Dr T J G Francis, which had been working with themAetomicf Energy Seismological Research Laboratory on the development of sea-bottom seismographs under NERC sponsorship. Its work on seismicity, and a feasibility study of electrical methods of off-shore prospecting, linked directly with the activities of the Global Seismology and Marine Geophysics Units and the Group, never more than five in total strength, remained in IGS for five years. At the end of 1974, its activities having concentrated on the seismicity of the mid-Atlantic ridge and the effects of earth tremors on deep-sea sediments, it was thought appropriate to transfer it to the Institute of Oceanographic Sciences.
During the early years of the 1970s the Division grew rapidly in size and capability due to major contracts with Government departments following the Rothschild report. Notable for its expansion was the Marine Geophysics Unit, which moved in 1973 from its womb in the Applied Geophysics Unit in Princes Gate to Edinburgh where it inhabited temporary premises at Braefoot Terrace and St Davids Street before moving into Murchison House in 1975.
In 1974 the two Continental Shelf Units — in Edinburgh and Leeds — were transferred to the Geophysical Division because of the increasing pressure of contract work for the Department of Energy in the North Sea and the interdependence of these units and the Marine Geophysics Unit in its completion. At this time the Division, with 114 scientific staff and 75 support staff, was the largest in the Institute.
The continued increase in the proportion of the offshore effort devoted to Department of Energy contracts made it clear that it would be desirable to separate the units most concerned with this Marine Geophysics and the two Continental Shelf units — into a separate division concerned with offshore work and this was effected at the beginning of 1976. The remaining four units continued as the Geophysical Division for only a year until further divisional reorganisation removed Engineering Geology to the new Special Surveys Division and added Hydrogeology to the Applied Geophysics, Global Seismology and Geomagnetism Units to form the Geophysics and Hydrogeology Division.
In the ferment of change which the last decades of the twentieth century seemed to engender, this grouping lasted for only five years before the demise of Special Surveys Division and the advent of a Geophysics Division under, once again, a Chief Geophysicist. This was Richard Haworth who was 'recruited' from the Geological Survey of Canada in 1983.