Person: Castelli, Benedetto Antonio
Benedetto Castelli was an Italian Benedictine who was a student of Galileo.
Mathematical Profile (Excerpt):
- Benedetto was not the name that he was given when he was baptised, rather it was Antonio.
- He took the name Benedetto in 1595 when he entered the Benedictine order.
- Castelli joined the Benedictine order in the monastery of Saints Faustino and Giovita in Brescia on 4 September 1595.
- At first Castelli was certainly one of Galileo's students, but later the two became close friends.
- When Castelli was sent to the Benedictine abbey of La Trinità della Cava in the Finestre Hills outside Cava dei Tirreni in 1607 he corresponded regularly with Galileo and, when he was in Brescia in 1610, he wrote to Galileo thanking him for the copy of Sidereus Nuncius Ⓣ(The starry messenger).
- It is now impossible to prove whether this idea occurred to both Galileo and Castelli at the same time, or whether this letter of Castelli made Galileo turn his telescope on Venus to see if it showed phases.
- It is of little consequence which scenario is correct, for in either case Castelli came up with one of the most important ideas of the time.
- Castelli continued to study mathematics with a view to becoming a teacher, making a deep study of the works of Euclid, Ptolemy, Theodosius and Archimedes.
- Castelli, therefore, requested a transfer to Florence where Galileo was based and, in 1611, he went to Santa Maria di Firenze, the Benedictine abbey (called the Badia) located in the centre of Florence.
- He discussed with Galileo his observations of sunspots and it was Castelli who suggested that Galileo might find them easier to observe by using a telescope to project the sun's image onto a sheet of paper.
- While in Florence, Castelli gave private mathematics lessons.
- In 1613 Castelli was appointed as professor of mathematics at the University of Pisa, succeeding Antonio Santucci, having been recommended by Galileo.
- Galileo replied to Castelli in a letter written on 21 December.
- There was no Benedictine convent so Castelli lived in Pisa in the Jesuati monastery of San Girolamo.
- In 1616 Bonaventura Cavalieri came to live in the San Girolamo monastery and he was taught mathematics by Castelli who introduced him to the ideas of Galileo.
- Castelli was careful in his teaching in Pisa, where he was forced to teach that the earth was stationary.
- This was an unpleasant experience for Castelli, who suffered severely from seasickness, and, despite his best efforts, the celatone did not achieve success.
- Castelli, and later Galileo, gave the Archduke their opinions.
- In 1624 Castelli's appointment as professor at Pisa was confirmed as one for life.
- In 1628 Castelli published Della misura dell'acque correnti Ⓣ(On measuring running water), his famous book on hydraulics.
- This second notion has not yet been fully acknowledged because Castelli only hinted at it by criticizing Giovanni Fontana's measurements of the Tiber and his use of the term 'acqua premuta'.
- The acknowledgment of the incompressibility of water was nonetheless an essential prerequisite of Castelli's mathematical formulation of the continuity law of running water.
- Galileo was in Rome in May-June 1630 attempting to get Dialogue Concerning the Two Chief Systems of the World - Ptolemaic and Copernican published; he was made very welcome by Castelli during his visit.
- In 1631, while in Pesaro, Castelli wrote to Galileo.
- By the time Castelli returned to Rome, he was very upset to discover that Galileo had been found guilty and condemned to lifelong imprisonment.
- Castelli became increasingly uncomfortable in his position in Rome.
- For example Castelli was a believer in the heliocentric system yet the Inquisition did not proceed against him.
- Unhappy and out of favour in Rome, Castelli attempted to move to be near to his friend Galileo.
- Dated 13 June 1637, it is a detailed report on the failure of Castelli's apparent attempt to move out of Rome and be closer to Galileo.
- For about a dozen years Castelli had been teaching at the University of Rome under the patronage of the pope (Maffeo Barberini) and his nephew (Cardinal Francesco Barberini), but at a general convention of Benedictines that year Castelli (who belonged to this order) had been appointed abbot of a convent near Padua with the duty of being in residence there; however, the decision was not implemented because of the opposition of the Barberinis.
- Benedetto in Foligno, of S.
- Benedetto and Luigi in Palermo.
- Despite having to remain in Rome, Castelli continued to do fine science and to keep in contact with Galileo.
- For example, in a 1637 letter to Galileo, Castelli describes experiments where a brick was half painted white and half black, then exposed to heat from a fire and to light from the sun.
- Among his other achievements, Castelli claimed first that the intensity of light varies as the square of the distance, and was the first person recorded to have invented a rain-gauge in 1639.
- Castelli did not publish his treatise.
Born 1578, Brescia (now Italy). Died 9 April 1643, Rome (now Italy).
View full biography at MacTutor
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Origin Italy
Thank you to the contributors under CC BY-SA 4.0! 
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- non-Github:
- @J-J-O'Connor
- @E-F-Robertson
References
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive
