into two parts) was completed. Pendulums and falling bodies Riccioli is credited with being the first person to precisely measure the acceleration due to gravity of falling bodies. Books 2 and 9 of the New Almagest Riccioli included a significant discussion of and extensive experimental reports on the motions of falling bodies and pendulums. He was interested in the pendulum as a device for precisely measuring time. By counting the number of pendulum swings that elapsed between transits of certain stars, Riccioli was able to experimentally verify that the period of a pendulum swinging with small amplitude is constant to within two swings out of 3212 (0.062%). He also reported that a pendulum's period increases if the amplitude of its swing is increased to 40 degrees. He sought to develop a pendulum whose period was precisely one second – such a pendulum would complete 86,400 swings in a 24-hour period. This he directly tested, twice, by using stars to mark time and recruiting a team of nine fellow Jesuits to count swings and maintain the amplitude of swing for 24 hours. The results were pendulums with periods within 1.85%, and then 0.69%, of the desired value; and Riccioli even sought to improve on the latter value. The seconds pendulum was then used as a standard for calibrating pendulums with different periods. Riccioli said that for measuring time a pendulum was not a perfectly reliable tool, but in comparison with other methods it was an exceedingly reliable tool. With pendulums to keep time (sometimes augmented by a chorus of Jesuits chanting in time with a pendulum to provide an audible timer) and a tall structure in the form of Bologna's Torre de Asinelli from which to drop objects, Riccioli was able to engage in precise experiments with falling bodies. He verified that falling bodies followed Galileo's "odd-number" rule so that the distance travelled by a falling body increases in proportion to the square of the time of fall, indicative of constant acceleration. According to Riccioli, a falling body released from rest travels 15 Roman feet (4.44 m) in one second, 60 feet (17.76 m) in two seconds, 135 feet (39.96 m) in three seconds, etc. Other Jesuits such as the above-mentioned Cabeo had argued that this rule had not been rigorously demonstrated. His results showed that, while falling bodies generally showed constant acceleration, there were differences determined by weight and size