Benedetto Castelli
(1578-1643)
Antonio Castelli was born in Brescia, Italy, in 1578 and took the name
Benedetto upon entering the Benedictine order*
in 1595. From perhaps 1604 to
1607 he lived in a monastery in Padua and studied under Galileo. Upon
receiving a copy of Sidereus Nuncius, in Brescia in 1610, he applied for
a transfer to Florence, where he arrived
in 1611. Castelli helped see
Galileo's Discourse on Floating Bodies through the press and published
the reply (largely written by Galileo) to the polemics against it. Castelli
was also active in the initial stages of Galileo's
sunspot research in 1612,
coming up with the method of projecting the Sun's image through the
telescope.
Upon Galileo's recommendation, Castelli was appointed professor of mathematics
at the university of Pisa in 1613. When the court was visiting Pisa, late that
year, Castelli was invited to dinner and became involved in a lengthy
after-dinner discussion about the merits of the
Copernican System.
Castelli presented Galileo's arguments about reconciling the Copernican theory
with certain biblical passages, e.g. in the book of Joshua. It was
this occasion that prompted Galileo to write a long letter to Castelli on the
subject of science and religion, which was later expanded into the Letter to
the Grand Duchess Christina. Both versions of the letter circulated in
manuscript, and the Letter to the Grand Duchess was printed in
Strasbourg in 1636.
Castelli moved to Rome in 1626 to become a consultant to the Pope on the
management of rivers in the Papal States (a perennial problem) and professor of
mathematics at the university of Rome. In 1628 he published the important work
on hydraulics, Della Misura dell'Acque Correnti, or "On the Measurement
of Running Waters," a book that may be considered the foundation of modern
hydrodynamics. Castelli also made important discoveries about illumination
(independently formulating the photometric law), vision, after-images, and
diaphragms in telescopes. He was also a pioneer in the study of differential
absorption of heat by different colors. To the end, he was a faithful friend of
Galileo.
Sources
Stillman Drake, "Castelli, Benedetto," Dictionary of Scientific
Biography, III:115-117. For Castelli's various researches, see the series
of articles by Pietro E. Ariotti: "Benedetto Castelli and George Berkeley as
Anticipators of recent Findings on the Moon Illusion," Journal of the
History of Behavioral Sciences 9(1973): 328-332; "Benedetto Castelli:
Early Systematic Experiments and Theory of the Differential Absorption of Heat
by Colors," Isis 63 (1972):79-87; "On the Apparent Size of the
Projected After-Image: Emmert's or Castelli's Law? A Case of 242 Years
Anticipation," Journal of the History of Behavioral Sciences
9(1973):18-28; "A Little Known early 17th-Century Treatise on Vision: Benedetto
Castelli's Discorso sopra la Vista (1639, 1669): Translation and
Critical Comments [by] Piero E. Ariotti," Annals of Science 30
(1973):1-30; "Benedetto Castelli's Discourse on the Loadstone
(1639-1640): The Origin of the Notion of Elementary Magnets Similarly Aligned,"
Annals of Science 38(1981):125-140.
Glossary Terms
Benedictine Order -- The Order of Saint Benedict
is a confederation of congegations of monks and nuns, not a centralized religious
order. Each monastary is an autonomous community following the
rule of Benedict of Nursia.
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