Time-keeping the speed of sound in Florence in the early modern period

Around 1620, the French polymath Marin Mersenne (1588-1648) pioneered the experimental determination of the speed of sound in air by means of two different techniques: the first one exploited his studies on echometry, while the second one involved artillery shots. The return time of a sound echo from a reflective surface, or the time elapsing between seeing the flash and hearing a fire shot, was measured by Mersenne first by the pulse heartbeat, and subsequently by the pendulum oscillations. Artillery shots were later reused by members of the Florentine Accademia del Cimento (1657-1667) to investigate both the speed of sound and light. The ingenuity of the experimenters laid not only in the choice of using this method to explore acoustics issues, but also in openly declaring the intention to use the speed of sound to practically calculate physical distances. Through the analysis of the original manuscripts belonging to the Cimento, kept at the National Central Library in Florence, this paper aims to reconstruct the history of such experimentalism. Particular attention will be paid to the measurement instruments used, which are illustrated both formally in the official publication of the Academy and informally in the unpublished papers. The presentation ultimately tries to underline how the systematic use of new instrumental devices in the third half of the seventeenth century enabled scientific practices to reach very high accuracy levels.