Googling finds:
Refuted in Wikiquote Talk:
So to summarize what we know, based largely on the research of KHirsch above, the quote was first used in print (and misattributed to Leonardo da Vinci) in a science fiction story published in 1975, The Storms of Windhaven. One of the authors, Lisa Tuttle, remembers that the quote was suggested by science fiction writer Ben Bova, who says he believes he got the quote from a TV documentary narrated by Fredric March, presumably I, Leonardo da Vinci, written by John H. Secondari for the series Saga of Western Man, which aired on 23 February 1965. If this is correct, then the quote may have been written by Secondari for the TV documentary, and Ben Bova incorrectly assumed that he was quoting da Vinci. Accordingly, the probable author is John Hermes Secondari (1919-1975), American author and television producer.
Followup:
However, I should mention that a 1976 edition of Contact Quarterly, a biannual journal of contemporary dance, improvisation and performance, cites Leonardo da Vinci’s Codex on the Flight of Birds as the source of the quotation. I don’t know where to get a translation of that Codex, but I imagine one must be available somewhere, so it can be checked. – Embram 16:15, 28 January 2012 (UTC)
- Having searched the ‘Codex on the Flight of Birds’ for the quote, nothing can be found that even closely resembles it. 2:22, 9 October 2013