A Jesuit timed falling objects with a choir chanting to a pendulum
In seventeenth-century Bologna, Giovanni Battista Riccioli dropped balls from the Asinelli tower while fellow Jesuits chanted in time with a pendulum to mark the seconds. The result was the first precise measurement of gravitational acceleration, confirming Galileo's rule that distance fallen grows with the square of the time.
Born in Ferrara on 17 April 1598, Riccioli joined the Jesuits in 1614 and studied at Parma, where the order ran a lively experimental programme and the astronomer Giuseppe Biancani, open to ideas like mountains on the Moon, inspired him. Denied his wish to be a missionary, he taught logic and physics, experimented with pendulums and in 1636 moved to Bologna as a theology professor. He admitted that once astronomy gripped him he could never put it out, and his superiors eventually assigned him to it officially.
His pendulum work was painstaking. Counting swings between star transits, he showed that small swings keep a constant period to within two swings in 3212, and that wider swings of 40 degrees run slower. Aiming for a pendulum beating exactly one second, which would make 86,400 swings a day, he twice recruited nine Jesuits to count and nudge the pendulum for a full 24 hours, getting within 0.69 percent. Dropping paired balls from the tower, he found a lead ball had fallen 280 Roman feet while an equally heavy wooden one managed 240, and blamed air resistance. He published diagrams so anyone could repeat his tests.
His 1651 New Almagest ran to more than 1,500 folio pages, covering everything from the celestial sphere to rival models of the universe, and became a standard reference across Europe, used even by the Protestant Copernican John Flamsteed. It weighed 126 arguments about whether the Earth moves. Riccioli noted that a spinning Earth should betray itself because the ground would move at different speeds at different latitudes.
His most lasting legacy is on the Moon: he introduced the naming scheme for lunar features still used today. He is also credited with discovering the first double star, corresponded with Huygens, Cassini and Kircher, and received a prize from Louis XIV. He died in Bologna on 25 June 1671, and asteroid 122632 bears his name.
Source: Giovanni Battista Riccioli
