After many vaine attempts to measure the circles made by coloured rays alone I at last thought of casting colours vpon a white paper, either by a speculum or immediatly by a Prisme which turned about its axis might make all yᵉ colours succed on yᵉ same pt of the paper; Or by casting integrated light on a paper wᶜʰ might bee varyed into all colours successively by stopping yᵉ rest. Then I laid the lentes so that they wanted 3 or 4 rings depth of touching.

(Transcription from Richard S. Westfall, communicated by I. B. Cohe, “Isaac Newton’s Coloured Circles twixt two Contiguous Glasses”, received 1964 August 31, in Archive for History of Exact Sciences, volume 2, issue 3, 1965 April 27, page 195.)