Page 225 - Art In The Age Of Exploration (Great Section on Chinese Art Ming Dynasty)

The torquetum is an invention of the thirteenth
century, devised in 1284 by Franco de Polonia or a
little earlier by Bernard de Verdun, and perhaps
ultimately inspired by an instrument invented by
the twelfth-century Islamic astronomer, Jabir b.
Aflah of Seville. It represents schematically the
several reference planes and circles of the celestial
and terrestrial spheres and enabled mechanical
solutions when converting coordinates between
the equatorial, ecliptical, and horizontal planes.
That is, it gave geometrical rather than mathe-
matical solutions to astronomical problems, but
not as with an astrolabe, which uses an analogue
system.
The planes represented, from the base upwards,
are: the horizontal; the equatorial, adjustable for
the latitude of the place of use; the plane of the
ecliptic, which is fixed to the equatorial plane at
an inclination of about 23.5°, depending on the
maker's data, and is engraved with a circumferen-
tial scale of degrees; and finally the vertical plane,
which can be rotated on the ecliptical plane over
which moves an alidade, with sighting vanes,
bearing the support for the vertical plane.
Martin Bylica's torquetum is engraved, like his
other instruments, in Roman antiqua script and is
certainly by the same maker as the rest of the
instrumentarium. The disc representing the ver-
tical plane has a circumferential scale, which is
used with an alidade equipped with sight-vanes;
from the center hangs a plumb-line and bob. A
horizontal sundial and a small compass are on the
base-plate. On either side of the sundial are paral-
lel racks for the adjustable supports of the equa-
torial plane.
This torquetum, which was probably made by
Hans Dorn of Vienna, resembles another designed
in 1467 by the astronomer Regiomontanus; he
described its use in a brief treatise. F.R.M. presumably a goat but much elongated. The the outer scales of degrees. Inside the zodiac cal-
"bodies" attached are of snakes and form the endar scale is a diagram of unequal hours, used
Capricorn band. One head holds what could be a in conjunction with the semi-diametrical rule —
fruit or the severed head of a snake between its normally on the front of the instrument, but eas-
jaws. The remaining tracery is based on what ily transferred to the back — as a sundial. Below
appear to be four goat's legs and hooves, an inter- the diagram is a "shadow-square" used to survey
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twined snake-pattern, possibly two rythons, a and reach observations and calculations which
ASTROLABE flaming torch, and two dolphins. A human head would otherwise require trigonometry.
decorates the top of the central pin which holds Within the central, six o'clock hour-circle of
late i$th century ? the components of the astrolabe together. the diagram is a coat of arms engraved with cor-
Perugia ? The symbolism of the overall design has not nucopic decoration: the shield is charged with a
brass, partially gilt been elucidated. As is usual, the tips of various doubled-tailed lion rampant, the arms of the
7
diameter 27.6 (w /s) pointed parts of the tracery represent the posi- Alfani family. There is a reference, as far back as
inscribed (on a scroll on the back): ALPHENVS: tions of a selection of apparently thirty stars. the seventeenth century, to an astrolabe sup-
SEVERVS GENIO SVO: ET COMMODITATI -F" Their names are engraved close by and the ecliptic posedly made by Piervincenzo Danti de' Rinaldi
references: Danti 1579, Conestabile 1848, 14-15;
Uzielli 1875, 300-304; Uzielli i88Q; Rohde 1923, circle is divided into the zodiacal divisions. The having been in the Alfani family collection. If the
90-92; Gunther 1932, 2:322-325, no. 171 limb of the mater is engraved with the customary Hamburg astrolabe, which was acquired in 1893
scales of degrees and equal-hour divisions (0-12, from Frau Margarethe Gaiser and which had
Museum fur Kunst und Gewerbe, Hamburg twice) and is attached to a suspension-piece, mod- passed through the collection of Frederic Spitzer,
eled in relief, representing a bearded head is indeed this instrument, then its eclectic nature
This planispheric astrolabe of the European Re- between two dolphins, with a pivoted ring. There and the fact that it surfaced in the later nine-
naissance is highly ornate and untypical. The trac- are six plates, engraved on either side, for a total teenth century would not be cause for concern.
ery of the rete (see cat. 121) is of zoomorphic of twelve different latitudes. The back of the Prof. Thomas Settle has generously shared
design, worked in relief. Each end of the Capri- astrolabe is engraved, conventionally, with a with us the following information concerning the
corn band terminates in the head of an animal, zodiac calendar scale (o° Aries, 10.5 March) within astrolabe's history. Ottavio Lancellotti (1593-

224 CIRCA 1492