12 SCIENCE PROGRESS 



predominance in the galaxy, then the theory of their independence 

 would fall to the ground. As a matter of fact, their distribution 

 is quite different from that of the other two classes. Instead of 

 being found chiefly in the Milky Way, they appear to avoid it, 

 and largely preponderate in the neighbourhood of the galactic 

 poles, although a few are found in the Milky Way. This 

 distribution might be supposed to indicate some connection 

 with our system, but this is not necessarily the case. If they 

 lie right outside it, it is quite conceivable that, in the direction of 

 the Milky Way, none are seen owing to the light which they 

 emit being scattered and cut off by the far-extending stars and 

 star clouds of the Milky Way. Further research will be 

 necessary before the question can be regarded as at all settled, 

 but at present the evidence, on the whole, seems in favour of it, 

 and it has the advantage of forming a connecting link between 

 some of our facts and of giving a coherent picture for our minds. 

 It may perhaps be mentioned that the very large line-of-sight 

 velocities that have recently been found for some of the spiral 

 nebulse may possibly indicate independence of our system. 



One always associates a spiral with the thought of rotation, 

 and it is undoubted that some at least of the nebulae are in 

 rotation. Attempts have been made to find whether our system 

 shows any evidence of rotation about an axis perpendicular to 

 the Milky Way. The problem is a very difficult one, involving 

 an accurate knowledge of the precession constant, and of the 

 magnitude and direction of the solar motion, in addition to 

 which it is complicated by the effects of star-streaming. It 

 is therefore not surprising that, up to the present, no concordant 

 results have been obtained beyond the proof that the rotation — 

 if it exists — must be very small in amount. The search for 

 a great central sun — the hub of the universe — about which the 

 whole system is turning is one that appeals strongly to man's 

 imagination, and several attempts have been made to discover 

 such. Madler decided upon Alcyone, the brightest star in the 

 Pleiades, but this supposition is untenable. If such a central 

 sun exists there is little doubt but that it must be situated in 

 the galactic plane, whereas Alcyone lies far outside this plane. 

 Easton, on the other hand, decided upon a centre situated in the 

 constellation of Cygnus, a rich galactic region containing many 

 nebulae. It has been mentioned above that, as a result of the 

 study of the distribution of stars in galactic latitude, it has been 



