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Léon FOUCAULT (1819-1868)

Talks and seminars by William Tobin relating to Léon Foucault.

Download Foucault's original publications.


Jean Bernard Léon Foucault was the French physicist who in 1851 set up an enormous pendulum in the Panthéon in Paris. The slow clockwise veering of the swing-plane of the bob demonstrated that the Earth was slowly turning anticlockwise below. In 1851 no one doubted that the Earth was spinning on its axis, but this first dynamical proof of the fact ended a quest that had begun in Galileo's time, over two centuries earlier. It established Foucault's fame then and subsequently. However, this was by no means his only significant contribution to 19th-century science. Others were:

This project, partly funded by New Zealand's Marsden Fund for curiosity-driven research, has produced a scientific and personal biography of Foucault which is as complete as possible within the limits of a book of readable length. Additional topics include Foucault's contribution to photography, his work as a journalist, and his search for fortune through mechanical regulators. The book is heavily illustrated, including 8 pages of colour plates.

The biography caters for three distinct readerships. The main text is accessible to the general reader with some scientific background---readers for whom terms such as velocity and mass do not need definition, but who may well have forgotten the exact definition of `sine.' Appendices provide maps, lists of Foucault's instruments in museums, and a sample of Foucault's writing. For readers with greater technical experience, a final appendix discusses the challenges involved in making a Foucault pendulum that is safe and which really does indicate the rotation of the Earth. (Many purported Foucault pendulums do not.) The book finishes with endnotes and citations to satisfy researchers in the history of science, and an index.

The French version, Léon Foucault: Le miroir et le pendule was published by EDP-Sciences in October 2002 as the first book in their collection Sciences et histoire. It won the Prix spécial du Jury of the Prix du livre de l'astronomie - Haute-Maurienne/Vanoise - Festival de l'astronomie 2003. (Citation)    In 2008, the whole Sciences et histoire collection was awarded the Plume d'Or of the Prix Jean Rostand. (Citation (pdf))

The English version, The Life and Science of Léon Foucault. The Man who Proved the Earth Rotates was published by Cambridge University Press in October 2003 and sold out in 2008. However on-line booksellers may still have copies in stock, while copies at greatly increased price have been advertised by second-hand booksellers.

Chapter titles (English version)

Preface (Dr David DeVorkin, National Air and Space Museum, Washington DC)
1. Introduction
2. Early years
3. The metallic eye: photography
4. The `delicious pastime' applied to science
5. The beautiful science of optics
6. Order, precision and clarity: reporter for the Journal des Débats
7. Mixed luck
8. The speed of light. I. Disproof of the corpuscular theory
9. The rotation of the Earth: pendulum and gyroscope
10. Biding time
11. The Observatory Physicist
12. Perfecting the telescope
13. The speed of light. II. The size of the solar system
14. Recognition
15. Control: The quest for fortune
16. Unfinished projects
17. Commentary
Appendix A. Maps and chronology
Appendix B. Extracts from the Journal des Débats
Appendix C. Photographs and instruments
Appendix D. Building a Foucault pendulum
Notes and references
Talks and seminars by William Tobin relating to Léon Foucault.

Articles of related interest

Some details of Foucault's work have been published elsewhere. See:

Some of the challenges involved in building a Foucault pendulum are outlined in Tobin & Pippard (1994) and Tobin (1996), and references therein. For a particularly nice treatment, see:

Invaluable advice is also given in numerous papers published in The American Journal of Physics, amongst which those by H.R. Crane deserve especial mention (e.g. 49, 1004-1006 [1981]; 63, 33-39 [1995]).

Download Foucault's original publications.

Sites of related interest

The Paris Observatory held a major exhibition on Foucault in 2002.

Hundreds of sites make reference to Foucault pendulums established around the world and can be found with a search engine. Notable sites include:

william @ bitbucket.tobin.fr (Edit out "bitbucket." and spaces which have been added to fool web crawlers)

Revised: 2014 December 10