Dear Mr. Mudd:
Q: What is an orrery, and how did Princeton University come to own one? How was it damaged in the Battle of Princeton?
A: An orrery is a mechanical model of the solar system. Orreries were regarded as essential teaching equipment for 18th-century lectures on “natural philosophy” (the physical sciences). Although invented ca. 1700 by George Graham, they have been called orreries because English instrument maker John Rowley named a copy he made of Graham’s machine “The Orrery” in honor of Charles Boyle, Earl of Orrery.
David Rittenhouse, a Pennsylvania clockmaker, self-taught astronomer, and later the first director of the U.S. Mint, designed and built the College of New Jersey’s orrery (now Princeton University). In 1771, College President John Witherspoon purchased it from Rittenhouse for approximately £220 and installed it in Nassau Hall. The orrery instantly became the College’s most valuable asset. Rittenhouse’s original plans for the orrery included a central panel of four square feet showing the planets revolving around the Sun, and two smaller panels, one focused on Jupiter and Saturn, and the other on the Earth and the Moon, but all that remains today is the central panel, after damages during the military occupation of Nassau Hall in 1776-1777. A more complete example of a Rittenhouse Orrery has been preserved at the University of Pennsylvania Library.