Dom Bédos de Celles

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François Lamathe Bédos de Celles de Salelles, known as Dom Bédos de Celles, (24 January 1709 – 25 November 1779) was a Benedictine monk best known for being a master pipe organ builder.

Life & work[edit]

He was born in Caux, Hérault, near Béziers, France. He was elected to the French Academy of Sciences at Bordeaux and correspondent of the Academy at Paris in 1758.

As a recognized organ-builder, he was called upon to carry out repairs and appraise and advise other organ-builders in many locations across France.

In 1760 he published "La Gnomonique pratique ou l’Art de tracer les cadrans solaires" under the patronage of the Jean-Paul Grandjean de Fouchy, Secretary of the Academy of Sciences and an authority in gnomonics and sundials.

In 1766-78 he published his treatise L'art du facteur d'orgues (The Art of the Organ-Builder). This monumental opus contains great historical detail about eighteenth-century organ building, and is still referred to by modern organ-builders.

He is buried in the former Abbey (now Basilica) of Saint-Denis.

Organ building in the mid 18th century[edit]

The 26 images below are taken from this work, kept in the St.Bernard's abbey library in Bornem.

Horizontal Sundial layout[edit]

The Dom Francois Bedos de Celles method (1790) otherwise known as the Waugh method (1973), enables a dial to be constructed on a narrower piece of paper or velum, than using Dürers (1525) method- though it is essentially the same for the hourlines 9 to 3. It relies on a theorem proved on 1682 by P. de la Hire.[1]

  • Starting at the bottom of the paper, a line is drawn across, and a vertical one up the centre. Where they cross is the point O.
  • Choose the size of the dial, and draw a line across. Where it crosses the centre line is F
  • Using the selected latitude. a line is drawn from O at this angle, this is a construction line.
  • Using a square, a line is dropped from F through the construction line so they cross at right angles. That point E is important. To be precise it is the line FE that is important as it is length .
  • Using compasses, or dividers the length FE is copied upwards in the centre line from F. The new point is called G and yes it is important- the construction lines and FE may now be erased.
  • From G a series of lines, 15° apart are drawn, long enough so they cross the line through F. These mark the hour points 9, 10, 11, 12, 1, 2, 3 and represent the points .
  • The centre of the dial is at the bottom, point O. The line drawn from each of these hour point to O will be the hour line on the finished dial.[2]
  • However, Dom Bédos de Celles had a unique way of marking up 7 and 8, and 4 and 5. Call the point where 3 crosses the line R, and a drop a line at right-angles to the base line. Call that point W. Use a construction line to join W and F. Waugh, in his book, calls the crossing points with the hours lines K, L, M.
  • Using compasses or dividers, add two more points to this line N and P, so that the distances MN = ML, and MP = MK. The missing hour lines are drawn from O through N and through P. The construction lines are erased.[2] The P. de la Hire theorem established that if a line is parallel to the 9 hourline, that is line WF then all the hourlines will be symmetrical around the hourline 6 hours later (i.e. 3). [1]

The method became well-known when it was adopted by Waugh, as the construction method to be used for horizontal dials by Albert Waugh, in his 1973 book Sundials: their theory and construction.[2]


  1. ^ a b Sawyer 2012, p. 35.
  2. ^ a b c Waugh 1973, pp. 38-39.


  • Sawyer, Fred (2012). "Horizontal Layouts 1-4". Compendium. Glastonbury, CT,USA: North American Sundial Society. 19 (11): 33–35. 
  • Waugh, Albert E. (1973). Sundials : their theory and construction. New York: Dover. pp. 38–39. ISBN 0486229475. 
  • Bédos de Celles, Francois (1760). "4-3". La Gnomonique pratique ou l'Art de tracer les cadrans solaires avec la plus grande précision (in French) (3 ed.). Paris. p. 459. Retrieved 12 July 2015. 
  • Dom François Bédos de Celles, L'art du facteur d'orgues (facsimile edition). Kassel / New York, Bärenreiter, 1963–65
  • Ferguson, Charles, The Organ-Builder. Translation of Dom François Bédos de Celles' L'art du facteur d'orgues. Raleigh, NC: Sunbury Press, 1977

External links[edit]