The article by Christopher Graney about the free-fall experiments of Giovanni Battista Riccioli opens a fascinating window on the work of one of the first modern physicists and his approach to devising a standard clock, finding its limitations, and using it to better determine fundamental laws of nature.
Not much has changed in the clock business since 1651. Unfortunately, the data on a falling clay ball, taken in painstaking detail by Riccioli and coworkers, is slightly misrepresented in Graney’s figure 5. The time axis should be in units of seconds, not in pendulum strokes as stated. If taken seriously, the graph conveys that the ball would have fallen more than 250 Roman feet (about 75 m) in 4.5 strokes of the pendulum, less than 1 second (1 second corresponds to roughly 6 strokes of Riccioli’s pendulum).
