The Romance of the Heavens 



other. But there are not quite as many stars going one way as 

 the other. For every two stars in one stream there are three in 

 the other. Now, as we have said, some eminent astronomers hold 

 that the spiral nebulas are universes like our own, and if we look 

 at the two photographs (Figs. 25 and 26) we see that these spirals 

 present features which, in the light of what we have just said 

 about our system, are very remarkable. The nebula in Coma 

 Berenices is a spiral edge-on to us, and we see that it has precisely 

 the lens-shaped middle and the general flattened shape that we 



FIG. 27 



have found in our own system. The nebula in Canes Venatici 

 is a spiral facing towards us, and its shape irresistibly suggests 

 motions along the spiral arms. This motion, whether it is 

 towards or away from the central, lens-shaped portion, would 

 cause a double streaming motion in that central portion of the 

 kind we have found in our own system. Again, and altogether 

 apart from these considerations, there are good reasons for sup- 

 posing our Milky Way to possess a double-armed spiral struc- 

 ture. And the great patches of dark absorbing matter which 

 are known to exist in the Milky Way (see Fig. 22) would 

 give very much the mottled appearance we notice in the arms 

 (which we see edge-on) of the nebula in Coma Berenices. The 



