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Alexander Thom

Long Meg and Her Daughters, the largest example of Alexander Thom's Type B Flattened Circle

Alexander "Sandy" Thom (26 March 1894 – 7 November 1985) was a Scottish engineer most famous for his theory of the Megalithic yard, categorisation of stone circles and his studies of Stonehenge and other archaeological sites.[1]


  • Life and work 1
  • BBC Chronicle – Cracking the Stone Age Code 2
  • Later use of his work 3
  • See also 4
  • Publications 5
  • References 6
  • External links 7

Life and work

Thom was born in Carradale in 1894. His mother was Lily Stevenson Strang from the family of Robert Louis Stevenson. Her mother (Thom's grandmother) belonged to a large family from Symington, upon whom had been bestowed the land by Robert the Bruce. His father was a clever tenant farmer at Mains farm for Carradale House. His father trained the Church choir while his mother was pianist. Thom spent his early years at Mains farm until moving to The Hill farm at Dunlop, Ayrshire. Instilled with a good work ethic by his father, Thom taught himself industrial engineering and entered college in Glasgow in 1911 where he studied alongside John Logie Baird. In 1912 he attended summer school at Loch Eck where he was trained in surveying and field astronomy by Dr. David Clark and Professor Moncur. In 1913, aged just 19, he assisted in surveying the Canadian Pacific Rail Network.

Thom graduated from the Royal College of Science and Technology and the University of Glasgow in 1914, earning a BSc with special distinction in Engineering. He suffered from a heart murmur and was not drafted during the First World War. Instead he went to work in civil engineering of the Forth Bridge and later designed flying boats for the Gosport Aircraft Company. In 1917 he married Jeanie Kirkwood with whom he shared a long and lively marriage. He returned to the University of Glasgow and worked as a lecturer from 1922 to 1939, quickly earning his PhD and DSc degrees. He built his own home called Thalassa in 1922, along with a windmill to power it with electricity. His father died in 1924 and he took over running the farm where he fathered three children, Archibald, Beryl and Alan. Thom helped to develop the Department of Aeronautics at Glasgow University and lectured on statistics, practical field surveying, theodolite design and astronomy. From 1930 to 1935 he was a Carnegie Teaching Fellow.[2] During the Second World War, Thom moved to Fleet in Hampshire where he was appointed Principal Scientific Officer heading the Royal Aircraft Establishment team that developed the first high speed wind tunnel.

He later was a professor and chair of engineering science at Brasenose College, University of Oxford where he became interested in the methods that prehistoric peoples used to build megalithic monuments. Thom became especially interested in the stone circles of the British Isles and France[3] and their astronomical associations. In 1955, Alexander Thom published A statistical examination of megalithic sites in Britain in which he first suggested the megalithic yard as a standardised prehistoric measurement. He retired from academia in 1961 to spend the rest of his life devoted to this area of research. The Thom Building, housing the Department of Engineering Science at Oxford, built in the 1960s, is named after Alexander Thom.

From around 1933 to 1977 Thom spent most of his weekends and holiday periods hefting theodolites and survey equipment around the countryside with his family member or friends, most notably with his son Archie. From studies measuring and analysing the data created at over five hundred megalithic sites, he attempted to classify stone circles into different morphological types, Type A, Type B, Type B modified and Type D flattened circles, Type 1 and Type 2 eggs, ovals and true circles. He suggested several were built as astronomical complexes to predict eclipses via nineteen-year cycles. Thom went on to identify numerous solar and stellar alignments at stone circles, providing the foundations for the scientific discipline of Archaeoastronomy. He further suggested the prehistoric peoples of Britain must have used a solar method of keeping calendar. Based on statistical histograms of observed declinations at horizon marks with no convenient star at −22°, +8°, +9° and +22° (except possibly Spica at +9°) between 2100 and 1600 BC, he suggested a year based on sixteen months; four with twenty two days, eleven with twenty three days and one with twenty four. Thom's suggested megalithic solar year was divided by midsummer, midwinter and the two equinoxes into four and then subdivided into eight by early versions of the modern Christian festivals of Whitsun, Lammas, Martinmas and Candlemas (see Scottish Quarter Days). He found little evidence for further subdivision into thirty two, but noted "We do not know how sophisticated prehistoric man's calendar was, but the interesting thing is that he obtained declinations very close to those we have obtained as ideal". Thom explored these topics further in his later books, Megalithic sites in Britain (Oxford, 1967), Megalithic lunar observatories (Oxford, 1971) and Megalithic Remains in Britain and Brittany (Oxford, 1978), the last written with his son Archie after they carried out a detailed survey of the Carnac stones from 1970 to 1974.[4]

Thom's ideas met with resistance from the archaeological community but were welcomed amongst elements of 1960s counter-culture. Along with Gerald Hawkins' new interpretation of Stonehenge as an astronomical 'computer' (see Archaeoastronomy and Stonehenge), Thom's theories were adopted by numerous believers in the lost wisdom of the ancients and became commonly associated with pseudoscience, which saddened him greatly.

In 1975, his wife, Jeanie died. In 1981 he underwent an eye operation and in 1982 he broke a femur falling on ice. He continued to write papers and undertook interviews and correspondence using a dictaphone with the assistance of audio typist, Hilda Gustin. He moved in with his daughter Beryl in 1983 in Banavie. Registered as blind, he concluded a final book Stone Rows and Standing Stones, a 557-page tome published posthumously with the assistance of Aubrey Burl in 1990. Alexander Thom died on 7 November 1985 at Fort William hospital, aged 91. His body was buried near Ayr.

His son Alan died in a plane crash in 1945 and Archie died in 1995 from a brain tumour. He is survived by his daughter Beryl Austin and grandchildren.

BBC Chronicle – Cracking the Stone Age Code

The Menhir Brisé suggested by Thom to have been once used for major lunar alignments in BBC Chronicle – Cracking the stone age code

In 1970 Thom appeared on a television documentary produced by the BBC Chronicle series, presented by Magnus Magnusson and featuring well known archaeologists, Dr. Euan Mackie, Professor Richard J. C. Atkinson, Dr. A. H. A. Hogg, Professor Stuart Piggott, Dr. Jacquetta Hawkes, Dr. Humphrey Case and Dr. Glyn Daniel. The programme discussed the difference between orthodox archaeology and the radical ideas of Thom. A pinnacle of his career, Thom finally got to publicly deliver his message on national television.[5] Despite the heavy criticism, he never vented his frustration on the archaeological profession as he said in the Chronicle program "I just keep reporting what I find".

Later use of his work

Thom's proposed length for the Megalithic yard has been reused as such in several controversial books that claim this unit of measurement is a subdivision of the Earth's circumference in an alleged 366-degree geometry. One such book is 'Civilization One: The World is Not as You Thought It Was', by Christopher Knight and Alan Butler who propose the 366 geometry theory.

Clive Ruggles has said that both classical and Bayesian statistical reassessments of Thom's data "reached the conclusion that the evidence in favour of the MY was at best marginal, and that even if it does exist the uncertainty in our knowledge of its value is of the order of centimetres, far greater than the 1mm precision claimed by Thom. In other words, the evidence presented by Thom could be adequately explained by, say, monuments being set out by pacing, with the 'unit' reflecting an average length of pace."[6] Royal Academy, that "The hypothesis of a smooth, non-quantal distribution of circle diameters (for Scottish, English and Welsh true circles) is thus rejected at the 1% level."[7][8]

Douglas Heggie casts doubt on Thom's suggestion as well, stating that his careful analysis uncovered "little evidence for a highly accurate unit" and "little justification for the claim that a highly accurate unit was in use".[9]

Euan MacKie, recognising that Thom's theories needed to be tested, excavated at the Kintraw standing stone site in Argyllshire in 1970 and 1971 to check whether the latter's prediction of an observation platform on the hill slope above the stone was correct. There was an artificial platform there and this apparent verification of Thom's long alignment hypothesis (Kintraw was diagnosed as an accurate winter solstice site) led him to check Thom's geometrical theories at the Cultoon stone circle in Islay, also with a positive result. MacKie therefore broadly accepted Thom's conclusions and published new prehistories of Britain.[22] In contrast a re-evaluation of Thom's fieldwork by Clive Ruggles argued that Thom's claims of high accuracy astronomy were not fully supported by the evidence.[23] Nevertheless Thom's legacy remains strong, Krupp[24] wrote in 1979, "Almost singlehandedly he has established the standards for archaeo-astronomical fieldwork and interpretation, and his amazing results have stirred controversy during the last three decades." His influence endures and practice of statistical testing of data remains one of the methods of archaeoastronomy.[10]

In his book Rings of Stone: The Prehistoric Stone Circles of Britain and Ireland. Aubrey Burl calls the megalithic yard "a chimera, a grotesque statistical misconception."[11]

In his book Genes, Giants, Monsters and Men, Joseph P. Farrell states, "If Thom is right, the development of human history will have to be rewritten." This Farrell surmises is why Thom encounters such opposition from certain groups.[12]

See also


Archaeoastronomical publications.

  • Thom, Alexander 1961 The geometry of megalithic man, Mathematical Gazette, 45, 83–93.
  • Thom, Alexander., Megalithic sites in Britain, Clarendon Press, Oxford, 1967.
  • Thom, Alexander., Megalithic Lunar Observatories, Clarendon Press, Oxford, 1970.
  • Thom, Alexander., Megalithic remains in Britain and Brittany, Clarendon Press, Oxford, 1978.
  • Thom, Alexander, Thom Archibald Stevenson, Burl, Aubrey., Megalithic rings: plans and data for 229 monuments in Britain, British Archaeological Reports, 1980, ISBN 978-0-86054-094-6
  • Thom, Alexander, Statistical and philosophical arguments for the astronomical significance of standing stones, in D.C. Heggie, Archaeoastronomy in the Old World, Cambridge University Press, 53–82, 1982.
  • Thom, Alexander, Statistical and philosophical arguments for the astronomical significance of standing stones with a section on the solar calendar, in D.C. Heggie, Archaeoastronomy in the Old World, Cambridge University Press, 53–82, 1982.
  • 1990. Thom, Alexander and Burl, Aubrey Stone Rows and Standing Stones: Britain, Ireland and Brittany B.A.R. 1990, ISBN 978-0-86054-708-2


  1. ^
  2. ^
  3. ^ Hutton, Ronald The Pagan Religions of the Ancient British Isles Blackwell Publishing 1993 ISBN 978-0-631-18946-6 p. 111 [1]
  4. ^
  5. ^
  6. ^
  7. ^
  8. ^
  9. ^
  10. ^ MacKie 1977, Gingerich 2000, Krupp 1979:18, Hicks 1993
  11. ^
  12. ^

External links

  • Thom's publications at the Astrophysics Data System
  • Biography
  • "Astronomy before History, by Clive Ruggles and Michael Hoskins, a chapter from the Cambridge Concise History of Astronomy, Michael Hoskin ed., 1999
  • Alexander Thom, obituary by D. C. Heggie, Quarterly Journal of the Royal Astronomical Society, Vol 28, No 2, p 178-182
  • BBC Archive – Chronicle | Cracking the Stone Age Code
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