William Herschel discovered NGC 3188 = H III-910 = h690 on 8 Apr 1793 (sweep 1038) and recorded "vF, pL, r, iF, some of the stars visible." John Herschel logged, "eF; pL; 30 arcseconds." (9 Feb 1831, sweep 323).

Ralph Copeland, LdR's observing assistant, logged on 5 Apr 1874 "vF, cL, R, gbM, * 15 m near the middle and several small stars near (within 2 or 3' foll), but does seem resolvable." One of these "stars" may be a very companion (NGC 3188A) just off the southwest side.

400/500mm - 17.5" (4/9/94): surprisingly faint, small, round, diffuse, unconcentrated except for extremely faint star superimposed at center or a very faint stellar nucleus, appears to have an irregular surface brightness. Two faint stars just off edges; a mag 14.5 star 0.6' NW of center and a mag 15 star 0.6' E of center also confuse the observation. Forms a close double with NGC 3188A 0.7' WSW (not seen).

Notes by Steve Gottlieb