William Herschel discovered NGC 4100 = H III-717 = h1084 on 9 Mar 1788 (sweep 816) and logged cF, mE about 5' long near the meridian [N-S], about a little sf." Caroline's reduction is 1.3' northeast of center. John Herschel made two observations, recording on 7 Mar 1831 (sweep 329), "pB; vL; mE in pos 166.5°; 3' long, 1' broad, vgvlbM. This cannot be either [NGC 4088] nor [NGC 4096], as neither of these agrees in its angles of position."

400/500mm - 17.5" (5/2/92): bright, very large, very elongated 3:1 NNW-SSE, 4.0'x1.5', large brighter core, faint stellar nucleus. The northern extension appears slightly brighter. Mag 8.2 SAO 44027 is 7' NW. Member of the M109 (NGC 3992) group = LGG 258.

Notes by Steve Gottlieb