Dantis numbers. On
the facade of the church of Saint Maria Novella in Florence, Egnazio Danti in
1572 designed and put an elaborate astronomical instrument from him called Il
quadrante Astronomico di Claudio Tolomeo (The Astronomical quadrant of Claude
Ptolemy), an armillary sphere and 4
sundials.
The
quadrant was so called by Danti because it was described by Ptolemy in the
Almagest.
It is
made by a plate of marble, with sides of The
quadrant was set at around The
instrument had been built for measuring the height of the Sun in its passage
across the meridian (the Suns rays are in this condition tangent to the faces)
: from this measure, made on the Equinoxes, it is possible to calculate the
value of the Ecliptic
inclination.
It also contains 3 solar clocks with
Babilonic hours (counted from dawn), Italic hours (counted from sunset) and
Astronomical hours (counted from noon).
Today
the quadrant has been moved and it is no more in its original position: I don't
know for what reason (perhaps for a restoration), when it was removed and where
it is.
The
bracket that sustained the quadrant is formed by two parts, one on the
other. The
superior part contains on the West side a writing in which Danti devotes the
tool to the COSM.
MED. MAGN. ETR. DUX NOBILIUM ARTIUM STU DIOSUS ASTRONOMIAE STUDIOSIS DEDIT ANNO
D. MDLXXII
On
the East side there is the writing where we may read the numbers that are of
interest to Divine Kumahs.
DILIGETI OBSERVATIONE PERSPEC TA TROPICOR DISTANZIA G. XLVI. LVII. XXXIX. L. ET
ANGULO SECTIONIS G.
XXIII. XXVIII. XXXXVIIII. That
means : with industrious
observations (I find) the distance between the Tropics (that is) 46°
These
numbers give, in the pure sexagesimal notation used by Ptolemy and also by
Danti, the value of the ecliptic obliquity and his double. The
angles are given writing the number of the degrees, of the arc minutes (primi),
of the arc seconds (secundi) and of
arc thirds (terti).
Then
23°
with
the precision (supposed, but not true) of
1 "tertius" = 1/60 of arc second , about 5 millionth of degree. Modern
calculations give for the value of the ecliptic inclination in 1572 the value
23.4948 = 23°
2941.3 : the error of Danti is
about In
the lowest part of the bracket, under the writings, we find two sundials facing
East and West with French hours (or
as Danti writes ore Franzesi), that is with the hours counted from midnight (
as in our local solar time). On
the facade of the church, that faces South, there are another two sundials on
the sides of the Quadrant: one with
seasonal hours (Danti writes unequal or Planetary hours), the other
with Canonical hours (system used
by the monks of the monasteries in the Middle Ages). All
the information that I have
reported come from two books
written by the well known Italian dialist Giovanni Paltrinieri: the beautiful book Meridiane e orologi
solari dItalia (Sundials and solar clocks of Italy) and a small but precious
booklet with only 34 pages, in
which Paltrinieri describes completely the sundials and the quadrant of Danti,
departing from the volume Trattato delluso e della fabbrica dellastrolabio
(Treatise on the use and on the making of the astrolabe ) written by Egnazio
Danti in 1569.
If
someone has interested I can send 4 photos of the sundials , taken on June 8th
2004 : the images are enough heavy (about 500-700 kb each) Gianni Ferrari
|
- Danti's numbers Gianni Ferrari
- Re: Danti's numbers Sara Schechner
- Re: Danti's numbers dkumah