The Torquetum - History
- The first known accounts of the torquetum
are those of Bernardus de Virduno (Bernard of Verdun) in the Tractus super totum astrologium3 and Franco
de Polonia (Franco of Poland). It is not possible to ascribe
priority to either since the date of Bernard's account is unknown.
earliest known manuscript of Franco's account is dated at 1284.4 Franco does appear to be the main disseminator of the instrument,
since manuscript versions of his account are much more common,
and other descriptions, up to the late fifteenth century, are
based on Franco's work. A mid-fourteenth century manuscript at
the Ashmolean Library of Oxford, based on Franco's tract,5 includes labeled construction diagrams, as well as a diagram
and description of the semis.6
A number of observations using the torquetum have been recorded,
beginning in the thirteenth century. Peter of Limoges used one
to measure the initial position of the comet of 1299 in the eighteenth
degree of Taurus.7 Jean de Murs, a Parisian astronomer
famous for introducing the Alphonsine tables to Medieval astronomy,
and exceptional in his time for his record of astronomical observations
made between c. 1318 and 1344, recorded the entry of the Sun
into Aries on March 12, 1318 using a torquetum. For this observation
he invoked the the authority of Alphonse X, thus becoming one
of the earliest advocates of these tables.8
- In the late fifteenth and early sixteenth
centuries Franco's description was superseded by a number of
new accounts, among the best known being those of Regiomontanus
(Johann Müller, 1436-76) was a German astronomer famous
for his tables of planetary motion as well as his important celestial
observations. In 1472 he made scientific observations of what
later became known as Halley's comet.9
instrument, as depicted in 1472, included a variety of scales
(like those found on an astrolabe) allowing the determination
of time, the position of the sun in the zodiac on a given day
etc., as does the instrument depicted by Gregor Reisch.
- Perhaps the best known account, and certainly
the most commonly reproduced image
of a torquetum, is that of Peter Apian (1495-1552) published
in 1532.10 Apian depicts a "back-to-basics" instrument
made of wood with just the required observational scales. This
instrument is also set for a fixed latitude.
illustration of comet observation published by Apian in 1532
includes a torquetum, collapsed into the horizon configuration,
and a cross-staff.11 In 1540 Apian published his second
major work, the Astronomicum Caesarium, including his
pioneering observations on comets. This was the first scientific
description of comets other than their positions in the sky,
describing the appearances of five comets (including Halley's)
and the fact that their tails always point away from the sun.12 A late observation in which a torquetum was involved was the
observation of Spica in 1575 by Landgrave William IV working
with Tycho Brahe.13
- Despite this late example of its usage as
an observational instrument, most scholars seem to consider its
popularity in the sixteenth century to be do to its other uses:
1) as a device to demonstrate the various coordinate systems
of Ptolomaic astronomy, 2) as an analog computer to inter-convert
measurements between coordinate systems without the use of tedious
calculations, and 3) as a demonstration of the owners astronomical
expertise and sophistication (the torquetum is, after all a very
impressive instrument). The most famous example of this last
usage is in the painting The French Ambassadors by Hans
Holbien the Younger (1533).14
- 3 Gillespie, Charles Coulston (ed.). Dictionary
of Scientific Biography Charles Scribner's Sons, New
York (1970-80) II p 24.
- 4 Hudson, p 624.
- 5 Giles Hudson, personal communication.
- 6 Gunther, R. T. Early Science in Oxford: v.
II, Astronomy. Oxford University Press, Oxford (1923) pp
35-7. The images here are from Gunther, apparently redrawn from
the original manuscript.
- 7 Hudson, p 624.
- 8 Gillespie, VII p 129, 130.
- 9 Azimov, Issac. Azimov's Biographical Encyclopedia
of Science and Technology 2nd ed. Doubleday & Company,
Inc. Garden City (1982) p 70.
- 10 Apian's Astronomicum Caesarium is now available on-line. The RARE BOOK ROOM site from the Bodleian Library at the University of Oxford has the book at http://www.rarebookroom.org/Control/appast/index.html. The torquetum, including construction diagrams, is shown on thumbnails 61-62 (November 2010). The entire book may also be downloaded as a pdf from the Vienna University Observatory rare book collection at: http://www.univie.ac.at/hwastro/ (December 2007).
- 11 Wolfschmidt, Gudrun. Planeten, Kometen, Finsternisse
- Peter Apian als Astronom und Instrumentenbauer in Peter
Apian: Astronomie, Kosmographie und Mathematik am Beginn der
Neuzeit. Polygon-Verlag Buxheim, Eichstätt (1995) p
- 12 Gillespie, I p 179.
- 13 Ibid, II p 404.
- 14 Images of this painting are avaialble on a variety of sites. One with very high quality images and closeups is the Web Gallery of Art site (December 2007). Click here to see an example of a closeup of the torquetum from this painting.
- © R. Paselk
- Last modified 29 January 2015