
As quoted in the essay "To Albert Einstein's Seventieth Birthday" by Arnold Sommerfeld, Albert Einstein : Philosopher-Scientist http://www.worldcat.org/title/albert-einstein-philosopher-scientist/oclc/311439 (1949) edited by Paul A. Schilpp (p. 102). The essay, originally published as "Zum Siebzigsten Geburtstag Albert Einsteins" in Deutsche Beiträge (Eine Zweimonatsschrift) http://www.worldcat.org/title/deutsche-beitrage-eine-zweimonatsschrift/oclc/183334232 Vol. III, No 2, 1949, was translated specifically for the book by Schilpp.
1940s
Variant: Since others have explained my theory, I can no longer understand it myself.