of some of the Nebula. 527 



scope, is probably due to its large extent; for the faintness of its 

 spectrum indicates that it has a smaller intrinsic brightness than 

 the nebulae already examined. The brightest of the three lines 

 was well seen. I suspected also the presence of the next in 

 brightness. No indication whatever of a faint spectrum. The 

 bright line looks remarkable, since it consists of two bright dots 

 corresponding to sections of the ring; and between these there 

 was not darkness, but an excessively faint line joining them. 

 This observation makes it probable that the faint nebulous 

 matter occupying the central portion is similar in constitution 

 to that of the ring. The bright line was compared with the 

 induction-spark *. 



[No. 4964. 2241 h. 18 H. IV. R.A. 23* 19 m 9 s -9. N.P.D. 

 48° 13' 57"*5. Planetary; very bright; pretty small, round, 

 blue.] 



With a power of 600 this nebula appears distinctly annular. 

 The colour of its light is greenish bluef. The spectrum formed 

 by the light from this nebula corresponds with that of 37 H. IV. 

 represented in fig. 5, Plate V. 



In the spectrum of this nebula, however, in addition to the three 

 bright lines, a fourth bright line, excessively faint, was seen. 

 This line is about as much more refrangible than the line agree- 

 ing in position with F as this line is more refrangible than the 

 brightest of the lines, which coincides with a line of nitrogen. 



[No. 4532. 2060 h. 27 M. R.A. 19 h 53 m 29 s 3. N.P.D. 

 67° 39' 43". Very bright; very large; irregularly extended. 

 Dumb-bell.] In Vulpecula. 



The light of this nebula, after passing through the prisms, 

 remained concentrated in a bright line corresponding to the 

 brightest of the three lines represented in fig. 5, Plate V. This 

 line appeared nebulous at the edges. No trace of the other 

 lines was perceived, nor was a faint continuous spectrum de- 

 tected. 



The bright line was ascertained, by a simultaneous comparison 

 with the spectrum of the induction-spark, to agree in position 

 with the brightest of the lines of nitrogen. 



* Already in 1850 Lord Rosse had discovered a connexion in general 

 plan of structure between some of the nebulae which present small planetary- 

 disks in ordinary telescopes, and the annular nebula in Lyra. His words 

 are, " There were but two annular nebulae known in the northern hemi- 

 sphere when Sir John Herschel's Catalogue was published; now there are 

 seven, as we have found that five of the planetary nebulae are really annu- 

 lar. Of these objects, the annular nebula in Lyra is the one in which the 

 form is the most easilv recognized." — Philosophical Transactions, 1850, 

 p. 506. 



f For Lord Rosse's observations of this nebula, see Philosophical Trans- 

 actions, 1844, p. 323 ; ibid. 1850, p. 507 and plate 38. fig. 13 ; ibid. 1861, 

 p. 736 and plate 30. fig. 40. 



