Facts like these lead astronomers to believe that the Milky Way has a definite relation with all the visible universe, that even the most distant nebula is not an outlying universe apart from ours, but all are parts of one vast stellar system. It is possible that the Milky Way, which we see as a great circle, double in one part, is really an immense spiral, and that we are nearest one curve of it, the great southern division which looks so bright. It may be that the spiral nebulae, vast though they are in terms of earthly measurement, are tiny models of one tremendous spiral which enfolds the universe with its coils. PRINTED IN GREAT BRITAIN BY BALLANTYNE, HANSON & CO. LTD. EDINBURGH AND LONDON