George Vertue. Notebook entry. 1731 [published in "Vertue Note Books Volume IV" in Walpole Society 24 (1935–36), p. 17], mentions a portrait of "a gentleman standing, his hand on a bust," which he saw on a visit to Cassiobury in 1731—apparently this picture.
Hermann Warner Williams Jr. "The Bequest of Jacob Ruppert." Metropolitan Museum of Art Bulletin 34 (July 1939), p. 166, ill. on cover, observes that it does not match the description of no. 707 in the Cassiobury sale, in which the sitter's left hand is placed on a marble bust.
"Sir Peter Lely's Collection." Burlington Magazine 83 (August 1943), p. 188, lists this picture, or another representing Sir Henry Capel, in the painter's estate sale of April 18, 1682.
Ellis K. Waterhouse. Letter. February 21, 1947, suggests that the bust mentioned in the Cassiobury sale may be "lurking under some very modern repaint".
Ellis K. Waterhouse. Letter to Elizabeth Gardner. March 31, 1947, observes that Lely only used these "gigantic busts" between about 1655 and 1660.
R. B. Beckett. Letter. April 21, 1948 [letter unlocated; transcript only], considers the Capel portraits "of course, very good".
R. B. Beckett. Letter. December 24, 1948 [letter unlocated; transcript only], dates it about 1660, possibly a little earlier; observes that there was a "half length" portrait of Sir Henry in Lely's sale, perhaps bought back by the family.
R. B. Beckett. Lely. London, 1951, pp. 14, 38, 70, no. 62, dates it about 1658; observes that the same bust is depicted in the portrait of the dwarf Richard Gibson (National Portrait Gallery, London).
N. J. Barker. Letter to James Parker. March 5, 1965, suggests that it may originally have been a marriage portrait; compares the iconography with Titian's "Allegory".
Oliver Millar. Letter to Mary Sprinson. July 31, 1978, recalls his notes on having seen it originally: "Very fine original".
Katharine Baetjer. "British Portraits in The Metropolitan Museum of Art." Metropolitan Museum of Art Bulletin 57 (Summer 1999), pp. 14, 20–21, ill. (color), mentions that it is still in its original frame; observes that when the picture was bequeathed to the Museum in 1939 the bust on which the sitter's hand rests was hidden under a recent repainting.
Katharine Baetjer. British Paintings in The Metropolitan Museum of Art, 1575–1875. New York, 2009, pp. 19–21, no. 8, ill. (color), figs. 13 (installation photograph of the Great Library at Cassiobury Park), 17 (before cleaning).