William Herschel discovered NGC 3491 = H III-21 = h807 on 11 Mar 1784 (sweep 164) and noted "vF, S. I could not be sure till I put on 240x." His position was ~50 seconds of RA preceding UGC 6088. On 23 Mar 1830 (sweep 242), John Herschel simply noted "eF; R" but he measured an accurate position.

400/500mm - 17.5" (3/22/96): faint, very small, round, 30" diameter, very small bright core. Located in a blank region bordered by brighter stars forming a circular pattern 16'-18' diameter. The brightest of these are mag 8 SAO 99401 10' SE and SAO 99398 12' SSE.

Notes by Steve Gottlieb