Ruskin, John (1909). "Introduction". In Cook, Edward Tyas; Wedderburn, Alexander Dundas Ogilvy (eds.). The works of John Ruskin. Vol. 35. London: George Allen; New York: Longmans, Green, and Co. pp. lxvi–lxvii. OCLC1097357632.
This detail needs to be researched. See Gregory Murphy's Letter to the Editor in the New York Times, June 2000 (next citation). Murphy says the first letter went to Mr. Millais, and it was a second letter that went to Effie. This same source mentions the actual letters are in the Bowerswell Papers at the Morgan Library in New York. But quick research didn’t find the actual letters to confirm with Murphy wrote.
Ruskin, John (1909). "Introduction". In Cook, Edward Tyas; Wedderburn, Alexander Dundas Ogilvy (eds.). The works of John Ruskin. Vol. 35. London: George Allen; New York: Longmans, Green, and Co. pp. lxvi–lxvii. OCLC1097357632.