Lewis Swift discovered NGC 3633 = Sw. VI-40 on 23 Mar 1887 and reported "vF; S; R; nearly between a pB star and a faint star." His position and description matches UGC 6351.

400/500mm - 17.5" (4/4/92): faint, fairly small, very elongated 3:1 WSW-ENE, weak concentration. A mag 14 star is off the west edge. Located 3.5' WSW of mag 8.9 SAO 118799. NGC 3640 lies 21' SSE. Member of the NGC 3640 group.

Notes by Steve Gottlieb