R.J. Mitchell discovered NGC 542 on 16 Oct 1855 with Lord Rosse's 72" while observing NGC 529 and 536 (discovered earlier by the Herschels). This nebula was shown on the sketch as Delta and Dreyer measured a micrometric position.

400/500mm - 17.5" (8/31/86): faint, diffuse, slightly elongated. Located 2.6' SE of NGC 536 in the HCG 10 = NGC 529-536 group.

Notes by Steve Gottlieb