"We'll Never Conquer Space". Essay by Arthur C. Clarke first published in "Science Digest" (June 1960); later published in Arthur C. Clarke "Profiles of the Future: An Inquiry into the Limits of the Possible", 1962, in Arthur C. Clarke "Voices from the Sky", 1965, and in Arthur C. Clarke "Greetings, Carbon-Based Bipeds!: Collected Essays, 1934-1998", 1999.
Philip Dormer Stanhope (4th earl of Chesterfield.), Charles Caleb Colton (1861). “Lord Chesterfield's advice to his son on men and manners. To which are added, selections from Colton's 'Lacon'.”, p.125
World Student Christian Federation, John Raleigh Mott (1898). “The World's Student Christian Federation: Origin, Objects and Significance of the Federation; the Convention at Northfield and Williamstown; Some Achievements of the First Two Years”