The conception of our galaxy set forth by Eddington in his book _Stellar Movements and the Structure of the Universe_ is that the Milky Way forms a ring around a central, slightly flattened cluster. This ring is supposed to rotate in equilibrium so that the stars may remain concentrated in the configurations they now form. Assuming the ratio of the two radii as one to five, and using Eddington’s figures of 2000 parsecs for the distance of the Milky Way, and 10⁹ suns as the mass of the inner cluster, the period and density may be computed and compared with those of the typical nebula placed at a distance such as will make the diameter the same as that of our system. The results are given in Table VIII. TABLE VII ======+========+============+==========+========================== d | α | Mass | Period | Density ------+--------+------------+----------+-------------------------- 10² | 10⁻¹ | 2.7 × 10⁵ | 9 × 10² | 1.4 × 10⁹ suns per cu. LY 10³ | 10⁰ | 2.7 × 10⁶ | 9 × 10³ | 1.4 × 10⁷ 10⁴ | 10¹ | 2.7 × 10⁷ | 9 × 10⁴ | 1.4 × 10⁵ 10⁵ | 10² | 2.7 × 10⁸ | 9 × 10⁵ | 1.4 × 10³ 10⁶ | 10³ | 2.7 × 10⁹ | 9 × 10⁶ | 1.4 × 10¹ ------+--------+------------+----------+-------------------------- TABLE VIII =======+==========+=========+============+==============+=========== | Distance | Radius | Mass | Period | Density -------+----------+---------+------------+--------------+----------- Nebula |6 × 10⁶ LY|6 × 10³LY|1.6 × 10¹⁰ S|5.4 × 10⁷ year| 5.6 × 10⁻¹ Galaxy | |6 × 10³ | 10⁹ | 2.5 × 10⁸ | 1.2 × 10⁻² -------+----------+---------+------------+---------------+---------- The velocities of escape would be about 280 km for the nebula and 170 km for the galaxy. Considering the problematic nature of the data, the agreement is such as to lend some color to the hypothesis that the spirals are stellar systems at distances to be measured often in millions of light-years. The computations by O. H. Truman[8] and by R. K. Young and W. E. Harper[9] of the motion of our system with respect to the spirals, based on the radial velocities of the spirals, are another and stronger argument for the hypothesis. [8] _Popular Astronomy_, =24=, 111, 1916. [9] _Journal of the R.A.S., Canada_, =10=, 134, 1916. The principal objection lies in their apparently systematic distribution with respect to the Milky Way. The matter is usually stated in the form that “spirals avoid the Milky Way.” There are less than 300 nebulae _known_ to be spiral in form. The greatest of them all is just on the border. It is suggested that the spirals seem to follow the distribution of the small faint nebulae. If this is true, the most that can be definitely stated is that they tend to cluster in certain regions of the sky, in one of which the north pole of the galaxy is located.