“Progress imposes not only new possibilities for the future but new restrictions. It seems almost as if progress itself and our fight against the increase of entropy intrinsically must end in the downhill path from which we are trying to escape.”

Interview with the Chicago Times, Feb. 14, 1881.

Source: Squaring the Circle (1913), p. 12

Speech at the Albert Hall (4 December 1924), quoted in On England, and Other Addresses (1926), p. 70.
1924

Source: The Faith of a Liberal', (1946), p. 438

1970 Nobel Peace Prize acceptance speech

In Encyclical Letter Spe Salvi http://www.vatican.va/holy_father/benedict_xvi/encyclicals/documents/hf_ben-xvi_enc_20071130_spe-salvi_en.html (30 November 2007) <br class="br">2007

As quoted in The God Particle (1993) by Leon Lederman – ISBN 978–0–618–71168–0
Context: The progress of science is the discovery at each step of a new order which gives unity to what had long seemed unlike. Faraday did this when he closed the link between electricity and magnetism. Clerk Maxwell did it when he linked both with light. Einstein linked time with space, mass with energy, and the path of light past the sun with the flight of a bullet; and spent his dying years in trying to add to these likenesses another, which would find a single imaginative order between the equations between Clerk Maxwell and his own geometry of gravitation When Coleridge tried to define beauty, he returned always to one deep thought: beauty he said, is "unity in variety." Science is nothing else than the search to discover unity in the wild variety of nature — or more exactly, in the variety of our experience.

An Old Chaos: The Emperor's Tomb (p. 35)
The Silence of Animals: On Progress and Other Modern Myths (2013)