There is also a legend that his first thoughts about the pendulum occurred as he watched a hanging lamp swing in the Cathedral at Pisa . The only problem is that the hanging lanterns were not installed until a few years after Galileo's first proposal for use of a pendulum to keep time (timekeeping was a major issue in the physics experiments he was conducting, so he would have been thinking about the problem seriously rather than idly while in church). (Pictures from M. A. Sullivan http://www.bluffton.edu/~sullivanm/pisa/pisacathedral.html) and http://web.kyoto-inet.or.jp/org/orion/eng/hst/romanesq/pisa.html)