The two most beautiful words in the English language are "check enclosed."
(Dorothy Parker (1893-1967), U.S. author and humorist. As quoted in The Late Mrs. Dorothy Parker, ch. 17, by Leslie Frewin (1986).
Said in the 1920s; Parker, trying to earn her living as a writer, was referring to the financial insecurity of the profession.)
The most distinct and beautiful statement of any truth must take at last the mathematical form.
(Henry David Thoreau (1817-1862), U.S. philosopher, author, naturalist. A Week on the Concord and Merrimack Rivers (1849), in The Writings of Henry David Thoreau, vol. 1, p. 386, Houghton Mifflin (1906).)