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.
Famous David Rittenhouse Quotes
Letter to Thomas Barton (Sep 20, 1756) as quoted by Florian Cajori, The Teaching and History of Mathematics in the United States https://books.google.com/books?id=mELQAAAAMAAJ (1890) p. 39.
An Oration delivered February 24, 1775, before The American Philiosophical Society held at Philiadelphia, for promoting useful knowledge in [William Barton, Memoirs of the life of David Rittenhouse, Somerset Publishers, Incorporated, 1813, 569] http://books.google.fr/books?id=L1oUAAAAQAAJ&pg=PA569