ON THE STRUCTURE OF THE UNIVERSE 13 



concluded that our solar system lies slightly to the north of the 

 galaxy, so that Easton's conclusion cannot be admitted. 



A more recent discussion by O. W. Walkey indicates that 

 Canopus may be the sidereal centre. Although further evidence 

 is necessary before this can be definitely asserted, yet this 

 supposition appears more reasonable than any previous one. 

 Canopus is the second brightest star in the heavens, its 

 magnitude being o-86. In general, it is safe to assert that the 

 bright stars are the near ones, but this is certainly not the case 

 with Canopus, whose parallax was investigated by Sir David 

 Gill. Using eighth-magnitude stars as comparison stars, Gill 

 found for it a zero relative parallax, and this careful determina- 

 tion therefore indicates that its parallax is the same as that 

 of the comparison stars — i.e. of the order of a few thousandths 

 of a second of arc. It follows from this that Canopus is probably 

 from ten to one hundred thousand times as luminous as the sun. 

 One feels that such a star, one of the greatest, if not the greatest 

 sun of which we have any knowledge, has a claim to our 

 consideration, as being very suitable for the sidereal centre. 



The position of our sun relative to the galactic plane can be 

 fixed, as far as its galactic latitude is concerned, with a consider- 

 able degree of accuracy from the counts of stars in various regions 

 of galactic latitude. The determination of our lateral displace- 

 ment relative to the plane is not nearly so easy. Were the Milky 

 Way a band of stars of uniform density the matter would be 

 comparatively simple, for it is obvious that the number of stars 

 in the Milky Way included within a range, say, of 5 of galactic 

 longitude would reach a maximum for the 5 which included the 

 centre of the Milky Way, and it would simply be necessary to 

 determine the direction in which the stars of the Milky Way are 

 the densest. The problem is complicated, however, and the 

 results obtained rendered uncertain by the local irregularities of 

 the Milky Way — the occurrence of regions of exceptionally great 

 star density, and the numerous branches leading off from the 

 main track. Fairly concordant results have nevertheless been 

 obtained by Walkey who has discussed the question, using 

 counts of stars down to various limits of magnitude and of 

 various types. He concludes that the sidereal centre lies 

 approximately on the 230 galactic meridian. Further investiga- 

 tions will be necessary to confirm this result, but at present it 

 may be taken as a first approximation. From this result, by 



