255
of the monks. The noon dial is made on a marble slab located on the corner of two
walls of the courtyard, about 10 meters high. The midday line is accompanied by
lines marking the hourly divisions and an analemma for mean time (Fig. 15.3).
28
This identification is possible thanks to its reference in Secchi’s Meridiana manuscript, containing the calculations of a sundial in Grottaferrata for the year 1876.
29
The marble slab is not perfectly exposed to the south, but it is turned 3°47′ to the
east. It is also not perfectly vertical but tilted backwards by 9′ 30″. Secchi compensated for the tilt of the slab by calculating a secondary latitude. The gnomon is a
1.073 meter long iron style with a diameter at the base of 19.72 mm,
30
while the
angle of the substyle height is 4° 12′. The difference in longitude from the Roman
College, expressed in time, is 45 seconds, a minimal difference, so the solar time of
Grottaferrata is very similar to that of Rome. Secchi calculated the location of the
quarter hour on both sides of the meridian line.
15.4.6 Cosenza Sundial (1875)
The sundial is a noon dial, located on the facade of the Palazzo Campagna, a stately
home, opposite the recently restored Cosenza Cathedral. There was no record of this
sundial until Ileana Chinnici identified a reference to it in a document in the Secchi
Papers at APUG: “Finally, (the Cosentine authorities) wanted a sundial and this was
made ex tempore” (Fig. 15.4).
31
The sundial marks the true solar noon thanks to a polar gnomon still in place but
presents neither an indication of the maker nor a signature.
Further evidence of the attribution of the instrument to Fr. Secchi comes from a
short article in the Cronaca di Calabria (Chronicles of Calabria) of 15 July, 1898
which reads:
A gift to the library. Tito Secchi – nephew of the illustrious Father Secchi – gave a gracious
gift to our library by donating the notes that that scientist used to mark the data and calculations necessary to install the sundial on the facade of the Campagna Palazzo. The gift was
accompanied by a beautiful letter from dearest Titus, who is a diligent official and a gentleman of high and noble sentiment.
32
28 Guerrieri, A, 2014.
29 APUG, Secchi Archive, 82A.13 - Meridiana - notes (33 f.). The manuscript was identified and
consulted in 2005 and 2011 by Maria Luisa Tuscano.
30 The sundial was calculated for a latitude of 41° 47′ 5″; the secondary latitude is 41° 56′ 35″.
31 APUG, 23.II. D, 64v. We thank Dr. Ileana Chinnici, historian of astronomy at the Palermo
Astronomical Observatory, for graciously providing the documentary reference.
32 Michael Chiodo, L’Accademia Cosentina e la sua Biblioteca, Cosenza, 2002, p. 112. The transcript of the Chronicle of Calabria was kindly made available by Dr. Michele Chiodo, whom we
also thank for the search of the manuscript mentioned.
15 Angelo Secchi and the Measurement of Time
of the monks. The noon dial is made on a marble slab located on the corner of two
walls of the courtyard, about 10 meters high. The midday line is accompanied by
lines marking the hourly divisions and an analemma for mean time (Fig. 15.3).
28
This identification is possible thanks to its reference in Secchi’s Meridiana manuscript, containing the calculations of a sundial in Grottaferrata for the year 1876.
29
The marble slab is not perfectly exposed to the south, but it is turned 3°47′ to the
east. It is also not perfectly vertical but tilted backwards by 9′ 30″. Secchi compensated for the tilt of the slab by calculating a secondary latitude. The gnomon is a
1.073 meter long iron style with a diameter at the base of 19.72 mm,
30
while the
angle of the substyle height is 4° 12′. The difference in longitude from the Roman
College, expressed in time, is 45 seconds, a minimal difference, so the solar time of
Grottaferrata is very similar to that of Rome. Secchi calculated the location of the
quarter hour on both sides of the meridian line.
15.4.6 Cosenza Sundial (1875)
The sundial is a noon dial, located on the facade of the Palazzo Campagna, a stately
home, opposite the recently restored Cosenza Cathedral. There was no record of this
sundial until Ileana Chinnici identified a reference to it in a document in the Secchi
Papers at APUG: “Finally, (the Cosentine authorities) wanted a sundial and this was
made ex tempore” (Fig. 15.4).
31
The sundial marks the true solar noon thanks to a polar gnomon still in place but
presents neither an indication of the maker nor a signature.
Further evidence of the attribution of the instrument to Fr. Secchi comes from a
short article in the Cronaca di Calabria (Chronicles of Calabria) of 15 July, 1898
which reads:
A gift to the library. Tito Secchi – nephew of the illustrious Father Secchi – gave a gracious
gift to our library by donating the notes that that scientist used to mark the data and calculations necessary to install the sundial on the facade of the Campagna Palazzo. The gift was
accompanied by a beautiful letter from dearest Titus, who is a diligent official and a gentleman of high and noble sentiment.
32
28 Guerrieri, A, 2014.
29 APUG, Secchi Archive, 82A.13 - Meridiana - notes (33 f.). The manuscript was identified and
consulted in 2005 and 2011 by Maria Luisa Tuscano.
30 The sundial was calculated for a latitude of 41° 47′ 5″; the secondary latitude is 41° 56′ 35″.
31 APUG, 23.II. D, 64v. We thank Dr. Ileana Chinnici, historian of astronomy at the Palermo
Astronomical Observatory, for graciously providing the documentary reference.
32 Michael Chiodo, L’Accademia Cosentina e la sua Biblioteca, Cosenza, 2002, p. 112. The transcript of the Chronicle of Calabria was kindly made available by Dr. Michele Chiodo, whom we
also thank for the search of the manuscript mentioned.
15 Angelo Secchi and the Measurement of Time