SECT. XXXVI. TWO CLASSES OF NEBUL2E. 409 



as that of Orion ; even with Lord Rosse's telescope the edges either 

 fade into a luminous mist, which becomes more rare till it is im- 

 perceptible, or end in a tissue of faintish flocculi, or in filaments 

 which become finer and more scattered till they cease to be 

 visible, showing that the real boundaries have not been seen. 



The other class of nebulas, vastly inferior in size, of definite 

 forms and great variety of character, are scattered through the 

 remote heavens, or congregated in a great nebulous district far 

 from the Milky Way. Many cling to stars like wisps of clouds, 

 others are exactly like comets with comas and tails ; but the most 

 definite forms are annular and lenticular nebulae, nebulous stars, 

 planetary and elliptical nebulas, and starry clusters. However, 

 there are two in the northern hemisphere differing from all of 

 these, which are described by Sir John Herschel as amazing 

 objects. One in Yulpecula is like an hourglass .or dumb bell of 

 bright matter, surrounded by a thin hazy atmosphere so as to 

 give the whole an oval form, or the appearance of an oblate 

 spheroid ; with a higher optical power its form is much the same, 

 but the brighter part is resolved into stars, and the hazy part, 

 though still nebulous, assumes that mottled appearance which 

 shows that the whole is a stellar system of the most peculiar 

 structure :. it is a phenomenon that bears no resemblance to any 

 known object. (Fig. 3, plate 8, and fig. .3, plate 9). The other 

 is indeed most wonderful, and its history shows the gradual 

 increase in the space-penetrating power of telescopes. To Messier 

 it appeared merely to be a double nebula with stars ; with Sir 

 William Herschel's telescope it presented the appearance of a 

 bright round nebula encompassed at a little distance by a halo 

 or glory, and accompanied by a .companion ; while in Sir John 

 Herschel's 20 feet reflector it appeared to " consist of a bright 

 round nucleus, surrounded at a distance by a nebulous ring split 

 through half its circumference, and having the split portions 

 separated at an angle of 45 degrees each to the plane of the 

 other." (Fig. 1, plate 10.) This nebula appeared to Sir John to 

 " bear a strong similitude to the Milky Way, suggesting the idea 

 of a brother system bearing a real physical resemblance and 

 strong analogy of structure to our own." 



This object, which disclosed to Lord Rosse the astonishing 

 phenomenon of spiral nebulse seen in his telescope, presents 

 the appearance of the fig. 1 in plate 10, in which the partial 



