James Dunlop discovered NGC 1751 = D 78 = h2705 on 24 Sep 1826 with his 9" reflector and described as "a small faint nebula, about 15" diameter, with a minute star slightly involved in the south side." His position is 12' ESE of this cluster. though this observation was missed by JH when compiling the GC. Dunlop's position is 12' ESE of the cluster. JH independently discovered this cluster on 12 Nov 1836 and logged "extremely faint, irregularly round; 2' diameter".

According to Wolfgang Steinicke, this is the faintest (at V = 14.5) of Dunlop's discoveries but it was much more prominent visually (described as a "fairly bright" using Zane Hammond's 24"). Also, 1996ApJS..102...57 gives V = 11.7, so Steinicke's magnitude may be from an erroneous source (same mag repeated in DOCdb).

600/800mm - 24" (11/18/12 - Magellan Observatory, Australia): fairly bright, fairly large, round, 1.3' diameter. Contains a slightly brighter core that is offset from the geometric center and an irregular halo. Two mag 15-15.5 stars were resolved at the edges and a couple of extremely faint mag 16-16.5 stars were occasionally resolved within the main glow.

Notes by Steve Gottlieb