The sequence of events to be expected in a mass of astronomical matter left solely to the influence of its own rotation has now been traced out with tolerable completeness.

Of the five uniformities of structure mentioned in our introductory chapter we have found that two fall naturally into their places in the scheme of evolution of a rotating mass, these two being the spiral nebulae and the binary and multiple stars. Two others, namely the planetary and ring nebulae and the globular and moving star-clusters, seem at least to be capable of explanation in terms of a rotational theory of evolution, although our interpretation of these formations was largely conjectural.

The fifth uniformity was that observed in the solar system, and for this no place has been found in the rotational scheme of evolution. It is true that we found (§ 257) that planets might possibly form out of the atmosphere thrown off equatorially from a rotating mass of gas, but several objections present themselves against any attempt to explain the origin of our solar system in this way–primarily the objection that the next stage in evolution ought to be for the central mass to break up into an ordinary binary star, whereas our sun and planets are not binary. Also the arrangement of the components of typical multiple stars such as can have been formed by rotation (cf. fig. 45, p. 265) does not in the least resemble that observed in the solar system.