198 ■ OBSERVATIONS ON NEBULA 



are the utmost limits of nebulous light perfectly and certainly visible, while 

 the line \ is about as far as it is suspected to extend. The line 1~ also encloses 

 a space suspected to be a little brighter than the surrounding parts. 



NeMa h. 1991. 



43. Things certain. — 1. A large nebula surrounding the star 22, not hitherto 

 noticed. (See Art. 17, Aug. 7 and 10.) 



2. A slight diminution of its light within the pentagon formed by the stars 

 15, 20, 27, 26 and 22. (Art. 17, Aug. 10.) 



3. It is more extensive on the northern than southern side, but its gradation 

 or concentration is evidently from all directions toward the bright star 22. 



4. (In the trifid nebula.) The particulars concerning the attachment of the 

 triple star to the skirts of the part, A, and of its eccentricity in other respects, 

 as mentioned in Art. 17, Aug. 1 and 9. 



5. The rift a suddenly shelves outwards and to the north, forming a tole- 

 rably definite boundary, as is indicated by the comparative closeness with 

 which the lines succeed each other. (See Art. 17, Aug. 10.) 



6. This boundary is convex inwards, or towards the stars 3 and 5. 



7. The gradation from light to darkness on the inner boundary of the portion 

 A., is somewhat more sudden than on that of the other two. 



8. And in all three, it is more sudden, on the inner, than on the outer boun- 

 daries. 



44. Nearly certain. — 1. The portion B extends down to the stars 2 and 21. 



2. It also runs up a little into the cleft /3, fading off very imperceptibly, 

 (Art. 17, Aug. 9.) 



3. The boundary of A. running down from the triple star, turns faintly off 

 at an obtuse angle at the star 19, while a portion of somewhat less intensity, 

 encompasses the star 25. This fact is expressed in Plate V., by the bending 

 of lines 2 and 3 at that point, and their proximity; the line 1 diverging from 

 them to the star 25. 



4. The upper extremity of A, between the stars 12 and 28, runs up to a 

 pretty sharp angle. 



5. (In the northern nebula.) A slight increase of intensity on the right 

 hand of the vacancy; it is enclosed by the line 4. (Art. 17, Aug. 10.) 



