248
validated in later years. Moreover, Clavius’s work was significant for the care with
which the works of other scholars were cited.
Clavius played a central role in the Gregorian Calendar Reform: he chaired the
commission chosen by Gregory XIII and shaped the way in which Luigi
Lilio (1510–1576)’s proposals were implemented. Matteo Ricci (1552–1610), his
student, would bring this tradition to the Far East, giving the missions there an
added cultural purpose in which gnomonics played a role.
Athanasius Kircher (1602–1680), like Clavius originally from Germany, moved
to Rome in 1633. There he continued the development of sundial science that
Clavius had begun, employing the works of the Roman architect Vitruvius and
drawing multiple connections to physical phenomena, in a triumph of Baroque creativity that is still amazing today. His interest in optics was shown with the design
of sundials using reflected and refracted light. He studied the movements of the
shadows due to the Earth’s periodic motion as cast on various objects, providing an
opportunity to meditate on the different circumstances in which the same phenomenon might be observed. Hour lines were mapped out onto the unusual surfaces of
the curious instruments that he devised, which became part of the collection in the
museum that bore his name. Kircher would assemble the results of his studies on
gnomonics in his seminal work, the Ars Magna Lucis et Umbrae: In Decem Libros
Digesta (The Great Art of Light and Shadow: A Summary in Ten Books) published
in 1645, and four splendid slate tables, which are kept today in the astronomical
museum of INAF - Rome Observatory at Monte Porzio Catone.
Leonardo Ximenes (1716–1786), from Trapani, Sicily, joined the Society of
Jesus in 1750. As an engineer and a professor of mathematics and geography (at his
request) at the University of Florence, his name remains indelibly linked to his
remarkable scientific undertaking of determining the secular variation of the ecliptic. To this end, he restored the ancient gnomon situated in the dome of the Cathedral
of Santa Maria Del Fiore in 1475 by Paolo dal Pozzo Toscanelli and laid out a
meridian in the transept there. Taking very precise measurements with these instruments, Ximenes managed to calculate a secular variation of 29“ per century; his
value is in fact lower than the actual value of 47” per century, but this work demonstrated the great sensitivity of this gnomonic instrument. He wrote a book on the
subject, Del vecchio e nuovo Gnomone fiorentino (On the Old and New Gnomons of
Florence), considered of great importance for the extensive general treatment of the
subject and as a notable achievement in the scientific history of Tuscany.
By the time of Angelo Secchi, advances in optical instruments had increased the
precision of the observation of the phenomena. In his Discorso sui recenti progressi
dell’Astronomia (Discourse on Recent Progress in Astronomy) (Secchi 1859),
Secchi wrote: “Today, the use of optical means gives thousands of times better precision with a comparatively small sized instrument. So, for example, a telescope
half a meter long will give a more accurate observation of the Sun than the enormous meridian line of Santa Maria degli Angeli in Rome or Santa Maria del Fiore
in Florence.”
Though one cannot be certain that Secchi’s scientific education and his interest
in the history of this topic were influenced by this particular work, we note that
M. L. Tuscano
validated in later years. Moreover, Clavius’s work was significant for the care with
which the works of other scholars were cited.
Clavius played a central role in the Gregorian Calendar Reform: he chaired the
commission chosen by Gregory XIII and shaped the way in which Luigi
Lilio (1510–1576)’s proposals were implemented. Matteo Ricci (1552–1610), his
student, would bring this tradition to the Far East, giving the missions there an
added cultural purpose in which gnomonics played a role.
Athanasius Kircher (1602–1680), like Clavius originally from Germany, moved
to Rome in 1633. There he continued the development of sundial science that
Clavius had begun, employing the works of the Roman architect Vitruvius and
drawing multiple connections to physical phenomena, in a triumph of Baroque creativity that is still amazing today. His interest in optics was shown with the design
of sundials using reflected and refracted light. He studied the movements of the
shadows due to the Earth’s periodic motion as cast on various objects, providing an
opportunity to meditate on the different circumstances in which the same phenomenon might be observed. Hour lines were mapped out onto the unusual surfaces of
the curious instruments that he devised, which became part of the collection in the
museum that bore his name. Kircher would assemble the results of his studies on
gnomonics in his seminal work, the Ars Magna Lucis et Umbrae: In Decem Libros
Digesta (The Great Art of Light and Shadow: A Summary in Ten Books) published
in 1645, and four splendid slate tables, which are kept today in the astronomical
museum of INAF - Rome Observatory at Monte Porzio Catone.
Leonardo Ximenes (1716–1786), from Trapani, Sicily, joined the Society of
Jesus in 1750. As an engineer and a professor of mathematics and geography (at his
request) at the University of Florence, his name remains indelibly linked to his
remarkable scientific undertaking of determining the secular variation of the ecliptic. To this end, he restored the ancient gnomon situated in the dome of the Cathedral
of Santa Maria Del Fiore in 1475 by Paolo dal Pozzo Toscanelli and laid out a
meridian in the transept there. Taking very precise measurements with these instruments, Ximenes managed to calculate a secular variation of 29“ per century; his
value is in fact lower than the actual value of 47” per century, but this work demonstrated the great sensitivity of this gnomonic instrument. He wrote a book on the
subject, Del vecchio e nuovo Gnomone fiorentino (On the Old and New Gnomons of
Florence), considered of great importance for the extensive general treatment of the
subject and as a notable achievement in the scientific history of Tuscany.
By the time of Angelo Secchi, advances in optical instruments had increased the
precision of the observation of the phenomena. In his Discorso sui recenti progressi
dell’Astronomia (Discourse on Recent Progress in Astronomy) (Secchi 1859),
Secchi wrote: “Today, the use of optical means gives thousands of times better precision with a comparatively small sized instrument. So, for example, a telescope
half a meter long will give a more accurate observation of the Sun than the enormous meridian line of Santa Maria degli Angeli in Rome or Santa Maria del Fiore
in Florence.”
Though one cannot be certain that Secchi’s scientific education and his interest
in the history of this topic were influenced by this particular work, we note that
M. L. Tuscano