LORD OXMANTOWN ON THE GREAT NEBULA IN ORION. 
G5 
Struve during his observations discovered a star (II.) which, strange to say, did not 
occur in Herschel’s list, although it was brighter than several small stars in this neigh- 
bourhood which were given in that list; nine days afterwards he saw it with difficulty, 
while the other stars had preserved their brightness. 
He repeatedly compared this star with 88, 51, 57, 75, 78, with the view of determining, 
if possible, the period of their variability, and gives the maximum and minimum bright- 
ness as follows, 88, whose brilliancy he found to be most constant, being taken as of the 
12th magnitude : — 
51 varies from 11*9 to 12-5 magnitude. 
57 
II. 
III. 
75 
78 
12*5 to 13-5 
11 '8 to invisibility. 
12*5 to „ 
12-0 to „ 
12-5 to „ 
98 he also considers variable to a certain extent ; and of the above list, II. he thinks is a 
variable star, whose maximum is of short duration and minimum of long duration, and 
7 5 one whose maximum is of a long and whose minimum is of short duration. 
Another instance of variability is IV., which Struve considers varies from the 11*5 
to 13*5 magnitude. 
With reference to the variability of the stars, our observations furnish very little 
information ; our attention was directed principally to delineating, as carefully as possible, 
the various details of the nebulae with reference to stars whose positions had been pre- 
viously determined. I may, however, remark that 29, to which Struve has assigned the 
same (7-|) magnitude as that of 20, 23, and 24, is now decidedly fainter than they are ; it 
is about the 11th or 12th magnitude. Herschel, on the other hand, gives the following 
magnitudes, 20=23=24=8th magnitude, 29=12th, which agrees with their present 
appearance ; 29 also is not quite in the same relative position as given in Herschel’s 
drawing ; he represents it nearly in the same line with 20, 23, 24, whereas the line through 
23, 24 is inclined through an angle of about 28 degrees from the line 24, 29. This 
discrepancy is probably due to an error in the position of 29, as Herschel places this 
star in his fourth or least accurately placed class. The discrepancy seems far too great 
to be accounted for in any other way. 
2. Variability of Form and Intensity of the Nebulosity . — On this subject it is impos- 
sible to speak decidedly. 
On comparing the following six drawings, — 
Sir J. Herschel’s of about the year 1825, 
Sir J. Herschel’s „ ,, 1837, 
Mr. Bond’s „ „ 1848, 
M. Liapounov’s „ „ 1850, 
Mr. Lassell’s „ „ 1854, 
Mr. Hunter’s „ „ 1863, 
MDCCCLXVIII. l 
