Galileo and the Altar Lamp Pendulum

IN 1583 Galileo Galilei (1564–1642), a youth of nineteen attending prayers in the baptistery of the Cathedral of Pisa, was, according to tradition, distracted by the swinging of the altar lamp. No matter how wide the swing of the lamp, it seemed that the time it took the lamp to move from one end to the other was the same. Of course Galileo had no watch, but he checked the intervals of the swing by his own pulse. This curious everyday puzzle, he said, enticed him away from the study of medicine, to which his father had committed him, to the study of mathematics and physics. In the baptistery he had discovered what physicists would call the isochronism, or equal time of the pendulum—that the time of a pendulum’s swing varies not with the width of the swing but with the length of the pendulum. This simple discovery symbolized the new age. Astronomy and physics at the University of Pisa, where Galileo was enrolled, had consisted of lectures on the texts of Aristotle. But Galileo’s own way of learning, from observing and measuring what he saw, expressed the science of the future. His discovery, although never fully exploited by Galileo himself, opened a new era in timekeeping. Within three decades after Galileo’s death the average error of the best timepieces was reduced from fifteen minutes to only ten seconds per day.

Daniel Joseph Boorstin, The discoverers (1983)

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