I do not design a machine which will give the ignorant in astronomy a just view of the solar system, but would rather astonish the skilful and curious observer by a most accurate correspondence between the situations and motions of our little representatives of our heavenly bodies and the situations and motions of those bodies themselves. I would have my orrery really useful by making it capable of informing us truly of the astronomical phenomena for any particular point of time, which I do not find that any orrery yet made can do.

Letter to Thomas Barton (Jan 28, 1767) as quoted by Florian Cajori, The Teaching and History of Mathematics in the United States (1890) p. 39.