Nebular and Stellar Spectra. 387 



of 14' 9 5 inches aperture, and 22*5 feet focus, under the direc- 

 tion of Gr. P. Bond, the worthy successor of his father ; and 

 at his death, Feb. 17, 1865, we are informed that he left a 

 MS. containing a thorough and systematic examination of the 

 nebula ; a work which continued to occupy his thoughts until 

 a few days previous to his decease. 



The Report of Harvard University, dated in the following 

 month, states that " during the winter and early spring of 1864-5, 

 minute observations were made on 59 nights, resulting in the 

 discovery of many new features." The astronomers engaged 

 assert that "it will require a long series of observations to 

 determine whether there are variations of the form of the 

 nebula, or of its light. It will also require many observations 

 to get more precise results about the variability of the stars in 

 the nebula." They think it a question whether the three ap- 

 parently well-defined groups of stars represented to the naked 

 eye as t, #, and c Orionis, may not be associated with the nebula 

 itself, rather than barely superposed, a point deserving of 

 notice being that many of the stars have nebulous envelopes. 

 It seemed to them highly probable that these three clusters are 

 coincident with three centres of aggregation of nebulosity ; and 

 they therefore extended their fresh survey 1^° N, and as far 

 S of 6, preserving nearly the same limits of B-A, 16' 52" * 

 each way. Within this area they have determined the places of 

 1143 stars ; the number in EPs and ^ 's catalogues having been 

 155, a difference arising in part from the enlarged extent. 

 " It has been found hardly possible to confirm S's supposed 

 discovery of variable stars, except in one or two instances. 

 The special difficulty arises from the fact that a bad state of 

 the atmosphere, and the consequent blending of the nebula 

 with small stars in its immediate neighbourhood, renders the 

 latter invisible." They have found 6, not identical with %\ 

 which show marked signs of change. They mention among 

 their other results, the tracing of the connection of c, and i } 

 Orionis, with 6, especially the great loop uniting i with 6, one 

 of the finest features of the whole nebula : the association of 

 the nebulosity with stars by general aggregation round the three 

 clusters — by wisps of nebula attached to certain stars — and 

 by larger numbers of small stars in bright nebulous areas, 

 contrary to the natural optical effect of a brighter ground : 

 the spiral structure of the parts surrounding 6 : and the com- 

 parative permanency of the form and aspect of the nebula, in 

 contradistinction to the rapid variations supposed by Otto Struve. 



These observations, so far as respects the extent and con- 

 nection of the whole nebulous mass, are in exact correspondence 



* There seems to be some mistake in these figures, which I am unable to rectify. 



