M31

The sky has been very good in the night of August 3 to 4, 1764; & the constellation Andromeda was near the Meridian, I have examined with attention the beautiful nebula in the girdle of Andromeda, which was discovered in 1612 by Simaon Marius, & which has been observed since with great care by different astronomers, & at last by M. le Gentil who has given a very ample & detailed description in the volume of the Momoirs of the Academy for 1759, page 453, with a drawing of its appearance. I will not report here what I have written in my [observing] Journal: I have employed different instruments for examining that nebula, & above all an excellent Gregorian telescope of 30 pouces focal length, the large mirror having 6 pouces in diameter, & magnifying 104 times these objects: the middle of that nebula appeared rather bright with this instrument, without any appearance of stars; the light went diminishing up to extinguishing; it resembles two cones or pyramides of light, opposed at their bases, of which the axis was in the direction form North-West to South-East; the two points of light or the two summits are about 40 minutes of arc apart; I say about, because of the difficulty to recognize these two extreminties. The common base of the two pyramides is 15 minutes [of arc long]: these measures have been made with a Newtonian telescope of 4 feet & a half focal length, equipped with a micrometer of silk wires. With the same instrument I have compared the middle of the summits of the two cones of light with the star Gamma Andromedae of fourth magnitude which is very near to it, & little distant from its parallel. From these observations, I have concluded the right ascension of the middle of this nebula as 7d 26' 32", & its declination as 39d 9' 32" north. Since fifteen years during which I viewed & observed this nebula, I have not noticed any change in its appearances; having always perceived it in the same shape.

Image is taken from here.

Extract from
Mem. Acad. for 1771, p. 446-447 (first Messier catalog).
[p. 457] 1764.Aug. 3. RA: 7.26.32, Dec: 39. 9.32.B, Diam: 0.40.
The beautiful nebula in the girdle of Andromeda.