(b. Mantua [?], Italy, ca. 1600; d. Rome, Italy, 1643)
Berti seems to have been a native of Mantua who spent most of his life in Rome. He was first mentioned (under the name of Alberti) as a distinguished mathematician who about 1629 collaborated with Francesco Contini in the mapping of the Roman catacombs. Berti’s friendship with Luc Holste, Athanasius Kircher, and Rafaello Magiotti suggests that he was born about 1600. In 1636, Holste described him to Nicholas Peiresc as an expert in mathematics and in the construction of mathematical instruments. About the same time, Berti’s observations of an eclipse came to the attention of Pierre Gassendi, who spoke of him as young, industrious, and erudite. Berti also refined the earlier observations of Christopher Clavius in order to determine the precise latitude of Rome; this he communicated to the English geographer John Greaves, who called him a celebrated astronomer. In July 1638, Magiotti informed Galileo that Berti had been recommended for a chair of mathematics by Benedetto Castelli, who considered him particularly well versed in the Galilean doctrines. Upon Castelli’s death in 1643, Berti was named his successor as professor of mathematics at the Sapienza, but died shortly afterward.
Berti’s historical importance, however, is in physics rather than in mathematics or astronomy. It was his experimental apparatus, constructed in Rome sometime between 1640 and 1643, that ultimately led to Evangelista Torricelli’s work on atmospheric pressure. Berti’s experiment seems to have been inspired by Galileo’s Discorsi (1638), in which it was asserted that water could not be raised more than eighteen cubits by a lift pump. Berti’s apparatus was described and illustrated in Magiotti’s letter to Marin Mersenne dated 12 March 1648. It consisted of a lead tube no higher than twenty-two cubits, bent downward at the top and terminating at either end in a valve sub-merged in a container filled with water. Magiotti stated that Berti, Who thought he had refuted Galileo’s statement, had improperly measured the distance from the water surface in the upper container to the floor rather than to the water surface in the lower container. Properly measured, Magiotti said, the height was indeed eighteen cubits. He went on to say that in writing of the experiment to Torricelli, he had suggested that if seawater were used, a lower level would result; and it was this suggestion that led to Torricelli’s experiments using mercury.
A more elaborate apparatus, which was attached to the façade of Berti’s house, is illustrated in Athanasius Kircher’s Musurgia (1650) and in Gaspar Schott’s Technica Curiosa (1664). It consisted of a lead tube about eleven meters long that terminated at its lower end in a valve and at its upper end in a globe, said to have been originally of copper and later of glass. From the juncture of globe and tube, a second lead tube that terminated in a valve was brought to a window about ten meters above the pavement. At Kircher’s suggestion, a bell that could be struck by a hammer activated by an external magnet was enclosed in the globe. The fact that a sound was heard convinced Berti that no vacuum existed; but, as Emanuel Maignan later remarked to him, the attachment of the bell to the tube could communicate the sound to the air outside.
Cornelis De Waard assigned to Berti’s experiment a probable date after the spring of 1639 (when Kircher returned to Rome after a long absence) and before 1642, taking a phrase in Magiotti’s letter to imply that Galileo was still living when the experiment was first performed. That implication is questionable, however, for the passage reads: “II Sigr Berti credeva conquest esperienza convincere il Sigr Galile…,” and convincere usually meant “refute” rather than “convince.” Probably the first experiment was performed not earlier than June 1641, when Torricelli left Rome, for it appears that he was informed of it by letter. The magnetic device escaped mention in both the 1641 and 1643 editions of Kircher’s Magnes, in which all manner of devices employing magnets were described and illustrated, which suggests that the elaborate apparatus was not earlier than 1643. Thomas Cornelius, recounting various Italian experiments of this kind in his Progymnasmata physica (1663), spoke of Berti as professor of mathematics at the Roman Academy when the experiment using the glass globe took place, which also suggests the year 1643. Torricelli’s mercury experiments of 1644 probably occurred soon after he received Magiotti’s first communication; if so, the various forms of Berti’s apparatus may all belong to the period 1642–1643.
All present knowledge of Berti is from secondary literature, which has been collected by Cornelis De Waard in L’ expérience barométrique. Ses antécédents et ses explications (Thouars, 1936), pp. 104 ff., 169 ff. Works cited herein and letters mentioning Berti may most readily be found in that work.