Messier 108

Discovered by Pierre Méchain on February 18 or 19, 1781.
Independently rediscovered by William Herschel on April 17, 1789.

Messier: M108.

(from the description of M97) Nebula near [M97 and Beta UMa], [position] yet to be determined.

Messier added a position by hand which was identified by Owen Gingerich in 1953 as that of H V.46 = NGC 3556, which is now called M108

(manuscript:) Nebula near the preceding .. it is even fainter: it is 48 or 49' further north and 30 min .. following in RA: Found by M. Méchain 2 or 3 days after the preceding [M97, which he found on February 16, so M108 was found on February 18 or 19, 1781]

Méchain

(in his letter to Bernoulli, May 6, 1783)
Page 265 No. 97 [M97]. A nebula near Beta in the Great Bear. Mr. Messier mentions, when indicating its position, two others, which I also have discovered and of which one is close to this one [this is M108], the other is situated close to Gamma in the Great Bear [M109], but I could not yet determine their positions.

William Herschel: H V.46.

V.46. Apr. 17, 1789.
vB. mE. r. 10' l, 2' b. There is an unconnected pretty bright star in the middle.
Very bright. Much extended [elongated]. Resolvable [mottled, not resolved]. 10' long, 2' broad. There is an unconnected pretty bright star in the middle.

[PT 1814]
V.46 [NGC 3556 = M 108] is "A pretty bright star in the middle of a very bright nebula, about 10 minutes in length and 2' broad."

John Herschel (1833): h 831.

h 831 = H V.46.
Sweep 324 (February 10, 1831)
RA 11h 1m 26.4s, NPD 33d 25' 0" (1830). [Right Ascension and North Polar Distance]
B; vl; pbr; vmE; pos 79deg.0. Has a distinct * in centre and 1 or 2 v S st elsewhere.
Bright; very large; pretty broad; very much extended; position angle 79.0 deg. It has a distinct star in the center and 1 or 2 very small [faint] stars elsewhere.

Smyth: CCCC [400]. H V.46

CCCC. 46 H. V. Ursae Majoris.
AR 11h 02m 02s, Dec N 56d 31.8'.
Mean Epoch of observation: 1835.29 [March 1835]
A large milky-white nebula, on the body of the Great Bear, with a small star at its sp [South Preceding, SW] apex, and an 8th-magnitude preceding [W] it at double the distance; there is also a brightish group in the np [North Preceding, NW] quadrant. It is easily found, since it lies only about 1 deg south-east of Beta, Merak. This object was discovered by H. [William Herschel] in April, 1789; and is No. 831 of his son's Catalogue. It is faint but well defined, being much elongated with an axis-major trending sp [South Preceding, SW] and nf [north following, NE] across the parallel, and a small star, like a nucleus, in its center. As H. [WH] considers this star to be unconnected with the nebula, it follows that it is between us and it, and therefore strengthens to confirmation our belief in the inconceivable remoteness of those mysterious bodies.

John Herschel, General Catalogue: GC 2318.

GC 2318 = h 831 = H V.46.
RA 11h 3m 3.0s, NPD 33d 34' 44.1" (1860.0) [Right Ascension and North Polar Distance]
eB; vL; vmE 79.0deg; pbM; r. 3 observations by W. & J. Herschel.
Extremely bright; very large; very much extended in position angle 79 deg; pretty bright toward the middle; mottled.

Rümker

Dreyer (1877)

M. Tempel, of the Observatory at Arcetri, near Florence, has made a considerable number of drawings of Nebulae with the two fine Amici telescopes at his disposal, which it is to be hoped may soon be published. The following Nebulae have, for the first time, been carefully drawn ar Arcetri: - GC .., 1949 [M 81], 1950 [M82], 2318 [M108], .., 4315 [M 14], ..

Dreyer: NGC 3556.

NGC 3556 = GC 2318 = h 831 = H V.46; G. Rümker.
RA 11h 3m 18s, NPD 33d 34.0' (1860.0) [Right Ascension and North Polar Distance]
cB, vL, vmE 79deg, pbM, r; = M108
Considerably bright, very large, very much extended in position angle 79 deg, pretty bright toward the middle, mottled.

Curtis

[Descriptions of 762 Nebulae ans Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 3556, RA=11: 5.7, Dec=+56:13. [Publ. Lick Obs.] Vol. VIII, Plate 26. An irregular, patchy spiral 8'x1.5' in p.a. 84deg; quite bright. Has a faint nucleus and shows a number of condensations, three of which are almost stellar; a star of magn. 11 near the nucleus. See Abs. Eff. 4 s.n.

Gingerich [Identification of M108]

Although Flammarion found Messier's notation of the position of the nebula near Gamma Ursae Majoris [..] he made no attempt to number it, and because Méchain did not give precise positions, Dr. Hogg omitted identifications of this and the other nebula near Beta Ursae Majoris. From my study of this region, the nebula near Beta is unambiguously NGC 3556, while an examination of the critical limiting magnitude of the catalogue indicates that the one near Gamma must be NGC 3992, a fact confirmed by the position Messier added to his personal copy. Thus, if the objects from M104 to M107 are included, it seems logical to me to number NGC 3556 and NGC 3992 as M108 and M109 respectively, especially as they are mentioned in the original catalogue.
[The identification of M108 is unambigous as Gingerich writes, but see for M109]