Practical Education Vol. 1, Maria Edgeworth and Richard Lovell Edgeworth 1798, London, p.55-56 link, (misidentified as a rainbow): "S-, a little boy of nine years old, was standing without any book in his hand, and freely idle; he was amusing himself with looking at what he called a rainbow upon the floor: [...] The sun shone bright through the window; [...] At last he found, that when he moved the tumbler of water out of the place where it stood, his rainbow vanished. [...] immediately observed, that it was the water and the glas together that made the rainbow. [...]"
leonardodigitale.com
Leonardo Da Vinci, Anatomical drawings at Windsor, folio 118r, ca 1508 link
