During the years of 1767-1770 David Rittenhouse designed and produced two orreries, one for Princeton Univ. and one for the Univ. of PA. During the last two years of this interval he also produced two 30-day musical tall-cased clocks. The first clock, built in 1769, is currently owned by the PA Hospital. The following year (1770) Rittenhouse made a second tall-case musical clock, which was more elaborate than the first. This clock, currently owned by Drexel Univ., is a very good example of Rittenhouse’s work as it has experienced only minor changes over the years. This was the masterpiece of his clock-making career and is a national historical treasure. Here is a detailed analysis of the various gears in the clock. 100+ drawings and full-color photos.