Fritz Leiber, 1951 (“Poor Superman”):
Everyone knows Newton as the great scientist. Few remember that he spent half his life muddling with alchemy, looking for the philosopher’s stone. That was the pebble by the seashore he really wanted to find.
Source: Heinlein, Robert A. (ed.), Tomorrow, the Stars, p. 208. SBN 425-01426-6, Doubleday & Company, Inc.