William Herschel discovered NGC 3955 = H II-623 on 21 Dec 1786 (sweep 660) and recorded "vF, S, E. Near the meridian but a few deg. from np to sf., a little brighter south of the middle." His position and description matches ESO 504-026.

400/500mm - 17.5" (5/11/96): fairly bright, moderately large, very elongated 4:1 NNW-SSE, 2.3'x0.6', broad concentration to a 1.5' diameter core. A mag 14.5 star is just preceding the NNW tip 1.1' from center. Located 4.7' SW of mag 8.9 SAO 180282. Probably a member of the NGC 4038/39 (Antennae) group.

Notes by Steve Gottlieb