(b. Rome, Italy, 31 August 1604; d. Florence, Italy, 20 January 1665)
In 1619, when he was only fifteen, Michelini entered the Piarists as a lay brother, under the name of Francesco di San Giuseppe. In 1621 the congregation was raised to the status of a religious order with the task of running free schools open to all, so that poor boys from their earliest years could be given both religious and secular education. The program of the order included a number of interesting teaching principles: religious instruction was not to take priority over other subjects; not only literature but also mathematics was to be taught; and all teachers had received a thorough training.
Michelini was therefore sent to continue his education in Genoa, where he studied mathematics with Somasco Antonio Santini. In 1629 he went to Florence, where the first schools of the order were to be opened, and took a letter (still extant) of introduction and recommendation to Galileo (from Giovanni Battista Baliani). One can follow his activities and movements until September 1641 through Galileo’s manuscripts, which contain several letters from Michelini; and he is frequently mentioned in other letters of the time, especially those of Benedetto Castelli, to whom Michelini was introduced by Galileo when he went to Rome in 1634. In April 1634 Castelli wrote to Galileo, who had already been obliged to retire to Arcetri: “I am amazed by his [Michelini’s] knowledge, surprised by the subtlety of his mind, delighted by the sincere love that he bears for you, and fascinated by his goodness,”
In 1635 Michelini was called to teach mathematics at the Florentine court, and a little later he was asked to give instruction to the brothers of Ferdinand II de’ Medici, Gian Carlo and Leopoldo—to whom he also gave lectures in physics and astronomy, which apparently were attended by the grand duke. In November 1636 Michelini was ordained a priest, and in 1648 he obtained the chair of mathematics at Pisa— vacant after the death of Vincenzo Ranieri—because negotiations with Ismael Boulliau and William Oughtred had failed. In his inaugural lecture, now lost, Michelini declared that all knowledge is derived from the exact sciences. Following this principle, he applied the experimental method even to medicine, in which he was much interested although he was not a doctor; he is generally credited with paving the way for Redi’s experiments and Borelli’s theories. Among other things he recommended the use in many illnesses of abundant quantities of orange and lemon juice, and advised people to control their weight. But being generally misunderstood, he was made the object of much derision.
In 1655 Michelini left the chair at Pisa and sought the appointment of Borelli, then at Messina, to replace him. In 1657, already in poor health and afflicted by gout, he received permission to leave his religious order and, remaining a simple priest under his old name, went to Sicily as a pro-vicar to the new bishop of Patti. The latter soon died, however, and Michelini had to return to Florence, in even worse health and with no financial resources. He had the good fortune, though, to attract the patronage of Prince Leopold de’ Medici, through whom, at the end of 1664, he was able to publish his book Della direzione de’ fiumi. A few weeks after its publication he became seriously ill and died within a few days.
In the following years books and papers by Michelini appeared in the possession of Vincenzo Santini—certainly not through inheritance, as was once believed—and in 1671 Santini copied from one of the books the marginal notes written by the young Galileo on Archimedes’ De sphaera et cylindro, comments that otherwise would have been lost.
Michelini was always reluctant to publish, and he left unpublished a number of “Discourses on Health,” now lost, which however were known at least to Redi, his direct follower in the field. As for the book he published just before his death, Michelini’s contemporary fame as an expert in hydraulics obviously did not depend on it. The relevant authorities had, many years before, sought his advice on important problems concerning water, such as the course of the Chiana River, the threat of silting in the Lagoon of Venice, and the control of the Arno for the protection of Pisa against floods. But now one can judge him only from his book, which has been much criticized because it includes several serious mistakes—for instance, the belief that stagnant water exerts pressure only on the bottom of its bed and not on the sides, even though Pascal’s basic principle of hydrostatics had been known for sixteen years. But since Michclini was dealing exclusively with running water, this error does not invalidate the rest of the work, which contains many good suggestions. One of them was that it should be possible to protect and repair riverbeds with boxes—or, rather, bulkheads—full of stones. Unlike Torricelli, he recognized the theory that one of the factors determining the velocity of current is the gradient of the riverbed. Most significantly, he attributed to the viscosity of water the fact that the current is faster in the middle of a stream than near the banks. This idea was not accepted by his contemporaries.
For these and for other reasons, Michelini was referred to as his partial source by Domenico Guglielmini when, in his fundamental treatise Della natura de’ fiumi (1697), he dealt with the control of riverbeds. This resulted in a reprint of Michelini’s book (Bologna, 1700) and its inclusion in all the editions of the Raccolta d’autori che trattano dell’acque, beginning with the Florence edition of 1723.
I. Original Works. Michelini’s surviving works are Trattato della direzione de’ Fiumi (Florence, 1664; 2nd ed., Bologna, 1700); and “Risposta alla scrittura del Sig. Torricelli,” in Raccolta d’autori che trattano del moto dell’acque, 2nd ed. (Florence, 1768), 121. His letters to Galileo are in Galileo, Opere, National Ed. (Florence, 1890–1909), XVI, 76, 139–140; XVII, 234–235, 316–317, 321–322, 399–400, 407, 411–412; XVIII, 35–36, 39–40, 128.
II. Secondary Literature. See the following, listed chronologically: G. Targioni-Tozzetti, Notizie degli aggrandimenti della scienze fisiche accaduti in Toscana nel corso di anni 60 del secolo XVII (Florence, 1780; repr. Bologna, 1967), I, 188–204, 365; P. Riccardi, Biblioteca matematica italiana, II (Modena, 1870), 156–157; and A. Neri, “II Padre Staderone,” in Rivista europea, n.s. 23 (1881), 756–764; and G. Giovannozzi, Scolopi galileiani, which is Pubblicazioni dell’Osservatorio Ximeniano dei PP. Scolopi, no. 124 (Florence, 1917); and “Un capitolo inedito della storia del metodo sperimentale in Italia di R. Caverni,” in Atti della Pontificia Accademia Romana dei Nuovi Lincei, 71 (1918), 171–189.