List 1-2013.pdf - Libreria Antiquaria Alberto Govi

former mathematics teacher and in 1575 Danti was told he had twenty-four hours to leave Tuscany. Danti had been working on a major
project at the time of Cosimo’s death, being he was in charge of the construction of canals to join Florence to both the Mediterranean Sea
and the Adriatic Sea. When Danti was forced to leave Florence this project, which was still at the planning stage, was abandoned. In 1574,
using his various instruments, Danti detected the 11 day error in the calendar when he calculated the vernal equinox to have fallen on 11
March rather than on 22 March as it should for the calendar to be in step with the seasons. From that time on Danti became a leading figure
in pressing for calendar reform and although his name is not associated with the final decisions on the Gregorian calendar, he was one of the
most important people to bring it about. After leaving Tuscany, Danti moved to Bologna in 1575, where Senate of appointed him Professor
of Mathematics at the university. From 1577 Danti accepted a commission from Ghisilieri, the Governor of his native city of Perugia, to
map the area around Perugia but this only took him away from Bologna for short periods and during this period he continued with his duties
at the University of Bologna. While he lived in Bologna, Danti continued his interest in astronomical instruments and he built a gnomon
at the cathedral. After completing his mapping of the Perugia area, he accepted a commission
from Pope Gregory XIII to map the Papal states. In 1580 Gregory XIII appointed Danti as
Papal Cosmographer and Mathematician and so he went to Rome where he also served on the
commission to reform the calendar. He undertook a range of other tasks in Rome including
being in charge of the painters working on the Vatican. He ended his career back in the church
being appointed Bishop of Alatri in Campagna in 1583. But another task he undertook just
before his death was to travel to Rome, at the request of Pope Sixtus, to assist the architect
Domenico Fontana, who had become architect to the papacy when Sixtus was elected, in
moving the Egyptian obelisk from its place in the circus of the Vatican. The obelisk had been
brought to Rome in the 1st century AD and Danti and Fontana erected it in 1586 where it now
stands in the centre of St Peter’s Square in the Vatican. After his return from this trip to Rome,
Danti contracted pneumonia from which he died.
His Trattato dell’uso e della fabbrica dell’astrolabio (1569) was the first book to be published
in Italy on the astrolabe and also contains the earliest known picture of woman using
a scientific instrument. In Le scienze mathematiche ridotte in tavole (1577) Danti produced a
compendium of mathematical knowledge including a summary of the fifteen books (now all
lost except the first) by his brother Vincenzo. Danti’s description of a machine he made to measure
the wind appears in Anemographia (1578). One of Danti’s most interesting publications
was Le due regole della prospettiva pratica di m. Iacomo Barozzi da Vignola (1583) which is
his commentary on Vignola’s perspective rules. His last publications was Trattato del radio
latino (1586), in which is described his surveying instrument (cf. I. Del Badia, Egnazio Danti
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