"Über das Unendliche" ["On the Infinite"] (1925) address to der Westfälischen Mathematischen Gesellschaft in honour to the memory of Karl Weierstrass, as quoted in "Number The Language of Science" by Tobias Dantzig, 1930.
Quoted in Alexander Macfarlane, Ten British Mathematicians of the Nineteenth Century (1916). "Pure mathematics; may it never be of use to any man!" is cited as the toast of the Mathematical Society of England in Science, 10 Dec. 1886.