LIST OF ILLUSTRATIONS 
PLATE FACING PAGE 
I The Great Nebula AT 31 in Andromeda 15 
II The Spiral Nebula N.G.C. 891 seen edgewise. ... 18 
III The Globular Cluster M 13 in Hercules 25 
IV Planetary Nebulae 27 
V Irregular Nebulae ......... 28 
VI Stellar Spectra 49 
VII Part of the Andromeda Nebula А/ 31 shewing resolution into 
stars .......... 331 
VIII The Central region of the Andromeda Nebula M 31 . . 332 
IX Elliptical and Irregular Nebulae 334 
X Normal and Barred Spiral Nebulae ..... 336 
XI Nebulae of late type 341 
XII The Spiral Nebula M 81 351 
XIII The Sequence of Nebular Evolution 355 
XIV Spiral Nebulae with nearly circular arms .... 357 
XV Spiral Nebulae with open arms ...... 358 
XVI Nebulae suggestive of Tidal Action ..... 405 
[Individual nebulae and clusters are indexed under their N.G.C. identi 
fication numbers in the general index (p. 424).]