166 OBSERVATIONS ON NEBTIL^ 



modes of examination and description more peculiarly adapted to this end than 

 such as can be employed in general reviews of the heavens. The observations 

 which are detailed in this paper are brought forward in illustration of this 

 inquiry. 



2. It will conduce to a clearer understanding of our object to point out, ge- 

 nerally and rapidly, the distinctions between our own theory of observation 

 and that commonly adopted. It consists not in an extensive review, but in 

 confining the attention to a few individuals; upon these exercising a long and 

 minute scrutiny, during a succession of evenings; rendering even the slightest 

 particulars of each nebula as precise as repeated observation and comparison, 

 with varied precautions, can make them, and confirming each more doubtful 

 and less legible of its features by a repetition of suspicions, which are of weight 

 in proportion as they accumulate; and, lastly, when practicable, correcting by 

 comparison of the judgments of different persons at the same time. 



Thus much for observation — for rendering the idea of the object as perfect 

 as may be in the mind of the observer. For the most unimpaired communi- 

 cation of this idea or perception, the theory of the process adopted is briefly, 

 1st. To form an accurate chart of all stars capable of micrometrical measure- 

 ment in and around the nebula. 2d. From these, as the greater landmarks, to 

 fill in with all the lesser stars, down to the minimum visible by estimation, 

 which, with care, need not fall far short of ordinary measurement. 3d. On 

 this, as a foundation, to lay down the nebula. After this preparation, subject 

 to no material distortion, except such digression from the original perception 

 of the observer as the difiiculties of accurate representation by a shaded ground 

 and subsequent copying and engraving may cause. Lastly, the process in- 

 cludes the adoption of a method of representing nebulse, intended to remove 

 the formidable and acknowledged difficulties just named, and at the same time 

 to introduce a niimerical precision in the manner of expressing on paper their 

 various features ; thereby transmitting the best impressions of observation with 

 almost unimpaired fidelity, and entailing only the necessary defects of original 

 vision. It is not supposed that this process, as more fully to be illustrated in 

 its application, is the best adapted to meet the end in view, for greater experi- 

 ence and reflection would certainly suggest particular modifications, if not ge- 

 neral alterations ; nor is it intended as a description of what has been done in 

 the present instance, but rather of what might be done, with more time, and 



