PHOTOGRAPHING THE STARS. 315 



object. It is indeed a unique spectacle in many respects, 

 one of which is that it alone of all the thousands of nebulae 

 is visible to the unaided eye. Many drawings of the 

 nebula in Andromeda have been made, and since the era 

 of powerful telescopes it was perceived that the spindle- 

 shaped nebulosity was marked by two remarkable dark 

 " lanes," parallel, or nearly so, to the length of the spindle. 

 These lanes are well shown in the later drawings of the 

 nebula, but they seemed devoid of significance till quite 

 lately. 



Dr. Isaac Roberts, on a favourable night, exposed to 

 the nebula for four hours one of the highly sensitive 

 plates that he uses ; and on developing and enlarging, 

 a picture was obtained which struck me at the time 

 I saw it, and which still appears to me, to be perhaps 

 the most instructive portrait of any celestial object I have 

 ever beheld. At once the significance of the mysteri- 

 ous lanes becomes apparent, and the structure of the 

 mighty nebula is for the first time disclosed. It is obvi- 

 ously a somewhat disc-shaped or rather lens-shaped mass, 

 tilted nearly edgeways towards us. The central portion 

 is especially brilliant and greatly condensed, and it is 

 surrounded by two or three rings of nebulous material. 

 The lanes are thus shown to be merely the better marked 

 portions of the divisions between these rings. They can 

 be traced nearly the whole way round in the photograph, 

 though, owing to the foreshortening, and the want of out- 

 line which is characteristic of nebulae, they become a little 

 confused at the extremities. The two other well-known 

 nebulae in the neighbourhood are also shown : they are 

 obviously parts of the same system. 



