Ralph Waldo Emerson (2010). “Essays and English Traits by Ralph Waldo Emerson: The Five Foot Shelf of Classics, Vol. V (in 51 Volumes)”, p.294, Cosimo, Inc.
"Newton and the Twentieth Century - A Personal View" by Hermann Bondi in "Let Newton Bel A New Perspective on his Life and Works" by R. Flood, J. Fauvel, M. Shortland, R. Wilson (p. 241), 1988.