In 1583 Galileo Galilei .. 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 time it took the lamp to move from one end to the other was the same. Of course Galileo had no watch, but he ckecked 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. He had discovered ... that the time of a pendulum's swing varies not with the width of the swing but with the length of the pendulum.
(Daniel J. Boorstin, American Historian, 1914)