10

OBSERVATIONS OF

Fig. 2, Plate II. H. IV . 41 =V. 10, 11, 12=h. 1991. R A. 17 h 52 m ; NPDllS 0 !'.

(17) I have been rather unfortunate in my figures of this nebula. That given in myNorthern Catalogue (fig. 80) is not to be taken as more than an attempt, and that a most rudeand imperfect one to show the situation of the fine triple star in its centre with respect to thenearer portions of the three principal surrounding nebulous masses. It is stated in theobservations recorded in that Catalogue, that a careful drawing made of the nebula was lost,and that the figure there given was constructed from much less elaborate sketches (in factthe rudest imaginable) aided by memory. The drawing from which my present figure isconstructed, was the work of a single night only (about the beginning of August 1835, for itbears no date, though the time can be ascertained nearly from other circumstances). Noprevious micrometrical measurements however having been procured of the stars involved andadjacent, wherewith to prepare a “ working skeleton” for laying down the nebula, bothnebula and stars were worked in by the unassisted eye, and although a series of angles ofposition among the principal stars was taken after the completion of the drawing (all singlemeasures), their results when subsequently projected, exhibited some material disagreementsfrom the eye-draft in respect of the situations of several of them inter se, and in one instance(that of the star marked k in the Catalogue annexed) the situation so projected proved quiteirreconcileable with the eye-draft, a discordance which however disappeared on supposing anerror of 5° to have been committed in one of the angles of position (from /3) by which it hadbeen determined. However as (allowing such an error to have been committed) the angles inquestion sufficed to fix the relative places of the six chief stars a fi e rj 6 k by directintersections, and of £ i X p v <f> y, each by a measured position from /3 combined withundoubted allineations among the other stars, on the whole in a tolerably satisfactory manner,there was little difficulty in inserting the other stars of the eye-draft so as to preserve theirconfigurations, and thence to lay down the nebula upon them without doing violence eitherto its general aspect, or to any important feature. Had the discordance in question beendetected before the final removal of the telescope it would have been easily rectified, but theoriginal drawing having been considered at the time satisfactory, it was put aside and notsubsequently re-examined and compared with the nebula itself, a circumstance the more to beregretted as this wonderful object, independent of its intrinsic interest, has also been made asubject of especial and elaborate examination by Mason in his paper already cited, illustratedwith a well-executed figure constructed from observations in the year 1839.

(18) On comparing our figures, they will be found to agree in every essential particularallowing for the difference of light between reflectors of 12 and 18 inches aperture, with onerather remarkable exception, viz., in the form of the southern mass of the trifid nebula and thecharacter of the curvature of the three paths or avenues which lead up to the triple star.Mason represents these avenues as free from any abrupt change of direction, the northernand the preceding of them branching out with an easy and graceful bifurcation from thesouthern: whereas my figure whose correctness in this respect I cannot doubt, gives to thepreceding avenue a remarkably sudden and uncouth flexure, like a gnarled branch of an oak,just at its divergence from the other two. The southern nebulous mass, in my figure, has aconsiderably wider extension towards the preceding side than in Mason’s which represents it as