Lewis Swift discovered NGC 1648 = Sw. III-31 on 29 Dec 1885 with the 16" refractor at the Warner Observatory and described "eeeF; pS; ee diff; nf of [NGC 1646]." His position is 19 tsec due east of PGC 15920 and the identification is certain though it's odd he didn't mention the nearby bright star!

400/500mm - 17.5" (1/23/93): extremely faint, very small, round, requires averted vision. A mag 11 star 3.3' SSW forms the vertex of a right triangle with NGC 1646 4.2' SW and 56 Eridani (V = 5.9) 7.4' WSW.

Notes by Steve Gottlieb